If the question "How does my body make blood?" leads you here: http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/lifecycle.html

and your child insists that you read and explain the diagrams.

Ladies, I DID NOT learn stuff like this in school.  I am going to have to do some homework. 

Oh- now he wants to know what holds his bones together (you know, like after they break and go back together).  Wish me luck!