connor herman and her colleague kyra ryan come into a family's home and take back the night. >> so glad to meet you. . >> reporter: sleep training small children is a booming business. the dream team charges close to $2,000 for an overnight stay like this and follow-up consultations. though they did not charge marchello and danielle for agreeing to let "nightline" tell your story. the method is controversial -- let your child cry, no matter how painful it is to hear. step number one, blackout the windows so the room is completely dark. step number two, turn on a sound machine to drouwn out any noise. and number three, put the baby to bed and walk away. >> we really believe after 4 months, children are ready to be successful swle fuful sleeping night. >> reporter: mia has been reading a story on the ipad about a baby that goes to. bed all on her own. but the book probably didn't prepare her for this. one kiss from mommy. >> just like little bear, mommy thinks you're ready to go to bed all by yourself. >> love you. >> reporter: what happens next is not for the faint of heart. [ baby cryin