C.P.
I agree with the responses so far. You might want to also try extending the "showing your son how to be nice to the cat" to include involving him in things the cat enjoys - let him give the cat some catnip or a toy to show him how much fun it can be to make the cat happy - or even just let him help you feed the cat. He'll see how good it feel to make the animal happy and maybe change his behavior. And don't worry about the cat - if it were that bothered, it wouldn't tolerate it.