Killing the snake was an insane reaction from the parents. A child getting a few pin-pricks should not result in a death sentence for the animal that did it. This was their own fault and completely avoidable. Unsupervised animal/child interactions simply shouldn't be allowed at all until the child in question is mature enough to understand how to behave appropriately around the animal. No matter how much you can trust the animal with yourself, you can't trust a 4 year old not to get excited and/or randomly do something crazy to set the animal off, plus of course any animal can also just plain have a bad day.
I have no doubt that the other snakes will be better off in new homes, but I bet the kids are going to be pretty unhappy at losing all the family pets, and they probably won't really understand the situation.
As far as the X-ray thing goes, I imagine that was done in order to placate the presumably hysterical parents. I rather doubt the doctor who ordered it actually believed it was necessary - it was probably the least costly test s/he could run that s/he felt would be "enough" to satisfy the parents that everything was being done for their daughter.
