I thought about posting how even most "naturalists" would be pretty horrified at the idea of a (human) loved one's body being used for animal food, and to little kids, the distinction between a beloved human family member and a beloved pet isn't always very clear. Then I thought maybe that was going too far, but since you brought it up...
I agree that your kids' perspective will most likely change as they grow up. No need to try to rush them in to it by making them aware of feeding their dead pet to the pet snake.
Oops, I have to go sooner than I thought so I'm not really done with this post. I'll probably add more later.