I think most people look at others in their life as "What can they do for me?" - including children - and you're right, once they aren't cute anymore they don't fill the need of the adult, so the adult stops trying. Sad. But I'd be willing to bet that's most often the case.

I've always lived by the belief that if you don't listen to children when they're little, they won't talk to you when they're grown. So I try to always talk and listen to children as the people they are, because that story they're telling me that's important to them when they're 9 will turn into an even more important one when they're 16, 25, 40.