You are quite correct. It seems to be the exception when a child star make it to a successful adulthood.I find being famous at a young age leads to questionable decision making and cockiness. Not everyone, but just in general.
Look at these people: Lindsay Lohan, Britney Spears, Jamie Lynn Spears, Justin Bieber, Miley Cyrus
All have done something questionable and have ruined their image to some extent.
Sure, it's cute when 12-year-olds are acting/singing, but when they get older you realize they have no talent. By that time they're already spoiled rotten.