I really wish breeders/pet shops took the time to make sure they were selling to people who understood how to provide the necessary care for the animal before purchase. Having enough money seems to be the only prerequisite. There are good breeders out there who care about the animals welfare over the cash, unfortunately they are the minority.
Loz, do as much reading about keeping that species in captivity as you can and teach your son as you go. Hopefully the snake will bounce back after treatment and hopefully vet bills won't be to bad. You will have to take a more active role in helping your son care for the snake. Best of luck.