>> reporter: winoenwynona rider the mother of the frantic boy. >> at that point we only had one scripthe really loved the script but it was a leap of faith on her part and without her, i don't think the show would have broken through the way it did. >> will, are you here? >> reporter: to find the right mix of younger stars. >> this isn't some lord of the rings book. >> the hobbit. >> reporter: they screened roughly 1,000 odditiaudition ta. >> just one bad child performance would -- i think it would destroy it. >> reporter: in a video posted by actress milly brown on twitter, the brothers witnessed her transform into the supernatural role of 11. >> 11, who is played by milly, because this is a character that doesn't have a lot of lines. but we were in a close up and went, oh, my god. >> reporter: judging from the online buzz and artwork created by fans, it already has a cult following. >> did you have any clue it would be as successful? >> we thought it would appeal to the people who, like us grew up loving these movies from the '80s. and that it would also work for a newer, younger gen