A snake as a pet?
Never in a lifetime. Not in my house.
I can't even watch snakes on TV.
That being said, I think that if your girls really, really like the snake, they should understand that perhaps the best thing for it is to let it go. Maybe it wouldn't be happy inside, in an enclosure. It's used to moving around freely outside. Also, snakes are cold blooded and neat heat to get their bodies and systems going.
If you are fine with your kids having a snake, I think you should really talk to a reputable pet store and discuss all that goes with owning and caring for one BEFORE you make the decision to go through with it.
It's just my opinion, but the one they caught should be set free to go back to his happy little life. That's part of the appreciation for nature.
Some reptiles are bred in captivity and I hear that they can make good pets.
I'll never know for sure, and I'm perfectly happy with that.
Best wishes.