Imagination of children

I have been watching Matthew these past few days and his new favorite toy is a Huggies box. He loves to crawl in and out of that thing, slide on it and whatever else he can imagine. It made me think of when I was little. I used to imagine so many things and could make something out of nothing all the time. I mean, I remember I used to play Barbie's all of the time and could come up with any kind of conversation for them and they would have a way cool life to live. Or I could look at a picture in a book and imagine what is going on or just make up what is going on. Or if you listen to children, they can tell you stories upon stories and you would have no idea where they came from. So, what I wonder is...what happens to us as we grow older? Do we just lose our imagination? Do we get so caught up in the "seriousness" of life that we can't do anything fun anymore? Sometimes I think it would be nice to go back to how it was when I was a kid and not have any worries anymore and just have fun. Just crazy thinking and wishes I guess.