I listened to Amy Bruckman give a talk about LambdaMOO some years back. She mentioned that kids frequently took much better to physical object-oriented metaphors than adults did. They might say things like "I don't understand why adults can't understand that a dog is-a animal, but a house has-a dog in it."

I think it's a great idea for a book. Send me a PM when it's published and I'll buy one :)