We visited my husband's parents in Oklahoma last week. They had a wonderful dry erase easel and the children were having a blast playing with it. The adults were sitting in the living room talking and when we looked up Michael had drawn a picture on the easel that looked just like the following photo except that his was done in carefully chosen colors.
He explained that this was a picture of the earth and showed us the crust, mantle, outer core and inner core and explained that it got hotter as you went further in. I was so proud of my four year old.
I knew exactly where he learned it. He's recently become obsessed with the Magic School Bus books. This is a series of books about a class of children and their teacher who has a magic school bus. The teacher takes the class for field trips in the magic school bus that cover a wide variety of non-fiction topics. His diagram of the earth came from the "Magic School Bus Inside the Volcano" book we had recently gotten from Scholastic Book Clubs. We've read it about 10 times since we got it.
The Magic School Bus books come in three varieties. The original picture books are aimed at ages 4-8ish and include some humor I find inappropriate for my younger children. There are also magic school bus chapter books aimed at older children. The version of the series we like are simpler picture books adapted for younger children by Scholastic. These feature the same set of eight children in each book so the kids get to know the characters. The humor is appropriate for younger children and school and classrooms are treated as fun places to be. You can find several of them on Amazon by searching for "Magic School Bus Scholastic Level 2."
I highly recommend these books. Michael (4) and Ava (almost 3) both really enjoy reading them over and over again and they're learning great facts at the same time.