I have two cats, and she's fine with them. As long as you have a secure top on, and whenever you take her out, you lock the cats out of the room, then there shouldn't be a problem. I have a thick metal screen lid with large snap ties holding it down(she likes to try to escape).
I feed her once every week or two (a gerbil, hamster, small rat, or three mice) I feed pre-killed. I don't like frozen since if the temperature in the snake cage isn't high enough, the rodent can start to rot in the snake's stomach before it is fully digested. You also sometimes get freezer burnt ones. The plus side is that freezing them kills off any bacteria or parasites, but I havn't had any problems with that at all. Feeding live can be dangerous since the rodent could bite the snake and cause infections. I find pre-killed is the best. I hate doing it though, since I love rodents.
If you are planning on getting your son a snake, I would recommend a corn snake. They are very good beginner snakes, are usually very well tempered, and eat well. Ball Pythons do not make good first pets(despite what some people think). They can be very finicky about eating (especially during the winter) I'm lucky to have a good eater, but I know someone who has one that didn't eat for 3 months as soon as she got it. We finally got it to eat, and now its doing great, but its not worth the hassle.