This is a nice book for children, and interesting for adults to browse too. I got this book as a gift when I was 8; doubt it's still in print, but a 2nd-hand copy would be worth picking up. It has sections on "Hardwoods and Evergreens", "Trees of the American Woods", "Trees of the Tropics", "The Medicine Trees" and "Some Historic Trees".
This book is filled with excellent B&W and full-colour watercolour illustrations & diagrams, and it conveys lots of ecological and historical info in a easily-readable way. Recommended.