parents there's no better toy than an ipad but what is it doing to your kid's brain? under fire. a district attorney and his wife murdered in cold blood. are white supremacists or drug carr tells to blame? the crime spree that is terrifying texas. and one of the strangest mating rituals in the animal kingdom. elephant seals and what humans can learn from the ocean beasts. >> announcer: keep it right here

>> announcer: from new york city, this is "nightline" with bill weir. >> happy and healthy are the stock answers most parents give when asked what they want for

their children when what they really want is for them to be quietly occupied. that was achieved through rocks and sticks and imagination and then through tv and now it is an ipad and smart phone. they are great distractions but what are the screens doing to all the growing brains? >> reporter: there are plenty of proud parents sharing their infant's touch screen skills on youtube. >> show me word world. >> where did it go? >> right there. >> good job. >> reporter: when it is taken away. you often get this. >> batteries run out. >> reporter: in a survey, 70% of parents admitted to letting kids use their user friendly devices. but some worry about what is it doing to their brain. the ipad didn't exist three years ago. so there is no hard data yet.

is it shrinking their i tension spans, ruining their eyesight or stunting social skills? >> five minutes. >> reporter: meet devon, delaney and dalton who is four. they are savvy digital divas. >> dalton -- can you hear me? dalton -- >> no. >> did you hear me? >> yeah. >> reporter: the klauss are from new jersey. >> when we go out we can whip them out and they will be distracted. >> what is that? >> the temple run. >> can you do it? >> theis three. >> reporter: we asked to see what they would do if they go ipad and iphone free far month. you heard me. cold turkey. >> say bye-bye.

>> bye ipad. >> bye iphone. >> say bye iphone. >> buy iphone. >> buy ipad. >> you can't play with them any more. >> reporter: the girls were left to play with their analog toys and had to resort to imagination play. >> what is that? >> this is my book light. >> you are pretending it's an ipad? >> yeah. >> reporter: and they fought a lot more. >> don't do that. >> reporter: to help us understand what we are seeing we went to barnard university's toddler center to observe kids reacting to traditional toys versus an ipad. the center tested something known as distractibilty. the kids aged 3 to 5 are given ipads to play with. the grown ups call their names to see how readily they respond. >> jackson what are you playing? jackson?

and lucas what are you playing over there? lucas? serena? what are you matching? serena. >> reporter: the only toddler who resisted to the magnetic pull does not tune out her environment. >> do you want to play with the ipad? no. >> reporter: the tablets are confiscated. >> you are sad? >> reporter: it seemed to the researchers that the toddlers are more verbal and social, more creative creatures. >> who likes pancakes? >> i like pancakes. >> reporter: this woman specializes in toddler development. the more you use a device to calm the kids down the less likely they will be able to do

it themselves. >> this is a way to stop them in their tracks. >> if you never learn that skill because you are pacified with an ipad you are not learning the skill of coming down from a tantrum? >> exactly. >> reporter: studies show that hours of screen time does not hurt kids's eyesight but is it associated with behavioral problems. but tablets are not passive. they are interactive. that is the intriguing twist. research just released show that toddlers learn better from interactive media. the team behind the "sesame street" characters have geared apps to be interactive. >> parents who give toddlers apps are terrible parents? >> that's wrong. i am creating content to encourage you to engage with your child and extend the

learning. >> reporter: apps can teach more than letters and numbers. >> what is that? >> apple. >> reporter: when a parent is involved it can be highly educational. >> you are not against free throw ninja and angry birds and apps out there? >> >> you are talking about trajectories and angles and force. but use descriptive language. >> angry birds as a physics lesson. >> angry birds as a physics lesson. >> reporter: nine-year-old devon has now learned an old fashioned craft. >> what did you realize? >> i had a free time to do that. >> reporter: but all that goes out the window when the girls are reunited with their digital devices. >> would you recommend it? going ipad free for a while? >> it's the amount of time you allow your kids to play with anything. how much time they watch tv and use the devices. >> if your child is the one who never looks up and is constantly

glued to it that is not a good thing regardless. if they have great social skills and still doing the play dates and getting outside and playing well with each other i think anything in moderation. >> reporter: ipads are like any other media for kids. parental discretion is advised. >> i win. >> reporter: for "nightline" i'm juju chang in new jersey. up next, a district attorney and his wife killed in cold blood. the murder that has officers of the court checking over their shoulders. >> announcer: abc news "nightline" brought to you by breathe right nasal strips. tuff. i can't breathe, so i can't sleep. and the next day i pay for it. i tried decongestants... i tossed and turned... i even vaporized. and then i fought back with drug-free breathe right. these nasal strips instantly open my nose, like a breath of fresh air.

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back in february it was a cop killer named christopher dorner who had law enforcement families across southern california double-locking their doors. tonight officers of the court and their loved ones in texas know that feeling of vulnerability after the murder of a district attorney and his wife and an assistant da proof that making an oath to keep the peace comes with a price. >> reporter: the details could be ripped from a legal thriller. >> we received a call of a possible two deceased persons. >> reporter: a veteran district attorney gunned down in his own home alongside his wife this weekend. >> we proceeded to the scene and found the district attorney mr. mclelland and his wife cynthia

deceased at that time. they both had been shot. >> reporter: kaufman county district attorney mike mclelland executed from multiple shots from an assault rifle and his wife cynthia murdered too. a brazen attack on a top law enforcement official is almost unheard of in small communities like this one. but weeks ago, mike mclelland himself stood before a bank of microphones and spoke to the unknown killers of one of his top deputies. mark hasse was shot outside the county courthouse in january by two suspects in black s.w.a.t. gear. >> i hope that the people that did this are watching because we're very confident that we're going to find you. we're going to pull you out of whatever hole you're in. >> reporter: instead of tracking down the killers, mclelland was gunned down as well. this is the third killing of a

public safety official in weeks unleashing a shock wave of fear. >> obviously we're under attack. we have seen two attacks in the last few months on district attorneys and other law enforcement officials. >> there is a certain vulnerability. >> i would be less than honest if i told you i was not worried. >> reporter: security at county buildings has been visibly increased. >> we are very much on alert. we have folks out to do harm to elected officials. and so we take that very seriously. >> reporter: the bold attacks have spurred a warning. >> the truth of the matter is if someone wants to kill you as a prosecutor it's very difficult to deal with that because we don't have security details. >> what are prosecutors telling each other and their staffs? >> the first thing they are doing this morning is reevaluating their security. every office i think at this point is concerned about that

and talking to law enforcement and their own investigators about what they need to do to protect themselves. >> reporter: but who would do such a thing? officials tell abc news they have few good leads. the county sheriff's department is taking the lead in the case. but dozens of investigators from the texas rangers, the fbi, atf and u.s. marshals have joined the hunt. prosecutors are look for motives and similarities in the cases including any possible links to the murder of colorado's chief of corrections gunned down at his front door two weeks ago. >> r.p. is saying that somebody rang the doorbell, the husband answered and was shot. >> reporter: evan ebel was a member of a white supremacist prison gang who escaped from colorado. >> he was going 100 miles an hour. >> reporter: mclelland said he made a dent in the aryan

brotherhood of texas and federal prosecutors indicted dozens of members of the group on melt pull charges of drug trafficking. in december law enforcement officials sent a bulletin saying that they planned to retaliate. >> if they can prove the aryan brotherhood of texas is involved it is carr tell like. they are capable of extreme violence against rivals and now maybe to public officials who are standing in the way of their business. >> a clear concern to individuals who are in public life, particularly those who deal with some very mean and vicious individuals, whether they're white supremacy groups or whether they're the drug carr tells that we have. >> reporter: whatever the motive behind the attacks, the ramifications are clear. >> it's not only an assault on those two and their families but

it's an assault on the rule of law and on the criminal justice system. and we've got to find them and find them quickly. >> reporter: tonight the street with the grisly murders have happened are back open. but now the people whose job it is to defend us now feel under assault. >> thanks. and coming up next, marvin gaye did not have this ritual in mind when he wrote those love songs. something you have to see to believe, next. my moderate to severe plaque psoriasis. i decided enough is enough. ♪ [ spa lady ] i started enbrel. it's clinically proven to provide clearer skin. [ rv guy ] enbrel may not work for everyone -- and may not clear you completely, but for many, it gets skin clearer fast, within 2 months, and keeps it clearer through 6 months. [ male announcer ] enbrel may lower your ability to fight infections.

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sure birds and bees are everywhere but it seems like in california mating rituals are a pillar of the economy. all the love scenes on the big screen and tabloids and all the elephant seals getting busy on the beach. this fascinating view draws hordes of tourists to the california shores every year. so nick watt went for a peek. >> reporter: if you drive down the coast of central california the right time of year you're in for a big surprise. you might spot ugly prehistoric looking beasts sunning themselves and having sex. this beach draws frisky elephant seals like daytona beach in spring. in november the dudes start arriving and fighting and the ones that win are the alpha

bulls. they have harems of 15 to 20 females. the beaten sneaker bulls loiter on the fringes hoping to see mating action when the alpha is distracted. and the humans gawk. >> what sort of reactions do you get from people who come here and see these monsters? >> very good question. we get everything from -- they are the ugliest thing i have seen to i really want to take one home. >> reporter: mother seals give birth on the sand and follows 28 days of suckling on 55% fat milk. they grow from the size of a seventh grader to a linebacker in less than a month and they are abandoned to fend for

themselves. >> i they instinctively go to the ocean to hunt. >> reporter: and they return to mate and molt on the same beach. >> there are few places that you can go to a place and see an animal who spends a chunk of life on "n" one place. >> reporter: and researchers are attaching data gathering devices on the animals. >> they don't stop for eight months. >> reporter: mankind nearly hunted these bizarre creatures out of existence. >> they thought they were extinct. they found 12 animals on the beach. not all the elephant seals were on the beach that day. >> reporter: the mexican government led the conservation charge and the seals bounced

back. >> one male could have been the father of all the northern elephant seals that exist today. >> reporter: they have been on the earth for 3 million years and we have been studying them for 40 years. we only found out that they swim as far out as the international date line and dive as deep as a mile below the surface. >> it's a wonderful animal. there are so many aspects from physiology and medicine to how they dive and handle pressure. >> reporter: they stop breathing when they sleep. and they can explore remote ocean depths and take the sensors to places we have never been. >> are they at all loveable? >> the answer is yes. their evolutionary cycle is such that as the humans evolve they

continue on the. >> reporter: elephant seals have been doing this for a millennia. our 5,000 pound beasts in the deep sea giving us an instinct we need into the health of our planet. i'm nick watt in california. >> i learned a lot there. it's time for tonight's closing argument. connecticut legislatures moved closer to a gun law that will enact background checks. what do you think? the absence of federal restrictions should states take matters into their own hands? tweet us @nightline. thank you for watching us on abc news. we are always a online at abcnews.com.