ferrets and cats?

As someone else has said, sometimes cats & ferrets get along, sometimes they don't. I would also suggest adopting one from a rescue, some rescues will also let you bring in your other pet to see how it will do with the potential adopted pet. Which may not be the best indicator of how well they will get along at home, but it's a start. I also wanted to point out that although ferrets are great pets & I love them, they are a lot of work. In my opinion much more work than a cat or even most dogs. They produce much more waste than cats & dogs, so one must clean their litter box more often. They need lots of attention if you want them to be happy, gentle pets. And they require special food and a cage (it's really unsafe to let a ferret roam the house when you are not directly playing/watching it). It may be too much of a responsibility for a 12 year old. I wouldn't get any animal for a child unless I was willing to do 100% of the care if they lose interest in it. Just something to think about before buying or adopting one.

My son had a ferret and we had 2 kittens at the same time. They got along just great! They played together all the time. I don't know if it makes a difference that all 3 animals were very young but they grew up together and it sure was fun to watch them play!

Getting along all depends on the animals in question. Some ferrets get along quite well with cats while others do not. To make this choice easier you could try adopting a ferret from a rescue group as most of those ferrets have been evaluated on their interaction with other household pets.