I would not let any young child hold any snake for fear that the snake will be harmed and the child may be bitten out of fear by both child and snake. Having said that, I have a juvenille 28" Cal King. He has never tagged me but has crapped on me LOTS. After owning him for a couple of months and either petting him in his tank or handling him, he decided that I was ok and now is gentle as a snake can be and seems to actually like being held. If you do the same, you will be fine.
I have shown snakes at schools in the past, and allowed the kids to stroke my specimens to demonstrate that they are neither slimy, aggressive or nasty.
I think that the operative thought here is be prepared, have your expectations in line and educate your children.
As a grade school boy in California, we caught gopher snakes and King snakes. I still save them from roadways etc. I have been bitten more times than I can count "saving" these beautiful creatures. Their little teeth will make you bleed a little but with almost no pain. If one of your kids gets tagged, it can be a great learning experience and doesn't have to lead to a phobia.
My boy Gobbles, is super nice and will let anyone handle him even though he is still a juvenille. However, I did the work handling him daily without fail until he figured out that Dana was a good guy after all.