I wonder about this all the time and I think a great place to start is with a creative environment. Since becoming a mommy, I'm constantly reminded of my own childhood. Back then, parts of my house would turn into a castle or maybe a spaceship. What I wished for the most was a window seat, where I could sit and let my long hair out the window, just like Rupunzel. 
The possibilities for making imaginative spaces for kids are endless. Here are few samples of some I love!

Chalkboard!! We need more chalkboard.
(This is my favorite room!)

Imagine how many puppet shows could happen here, and what a great place to hide! I'm getting way too excited about this aren't I? Maybe, I'm the one who really likes these rooms and use inspiration for kids as an excuse.

I'm crazy about this color scheme. Its mature and fun at the same time! 
Special disclaimer: I'm not one for skipping out on listing my sources. Currently, I'm away from my personal computer and don't have any of the links. That was a big DUH, on my part. Promise to get them up as soon as I get home.