Are some genres "for kids"?

Moving this from the Whedon thread:

A smidge off-topic, but I don’t think children’s books/movies that are well done can ever be considered off limits to adults. I was a bit too old for The Outsiders and Judy Blume books when they became popular. Last year, I decided it was high time to correct this deficiency, and I read The Outsiders and Are you there God? It’s Me, Margaret . I loved them both.

I’ve heard people use the phrase “Stay gold, Ponyboy,” and I always thought it sounded cheesy. Now? I tear up just a little bit.