What is the name of this children's book?

When I was a kid, one of my favorite books to check out at the library was about this family who lived in space (maybe on a spaceship?). It tells about the parents telling the children stories about earth, about gravity, animals, the sky, etc. At the end of the book, they come back to earth, but it is the first time the children have seen earth. The story tells about what the children think about gravity, and animals, etc. I'm not sure if it's supposed to be set in the future, or in an alternate reality. It's a really good book, but I can't remember what it's called or who wrote it. It's a kid's book, with lots of illustrations. If anyone knows the name of this, book, please let me know! I'd really appreciate it! :)