Never hit your cats, it is really cruel and accomplishes nothing, so never ever hit your cat. Talk in full sentences to your cats, if the cat will not listen, keep a squirt bottle of plain water handy. Keep that water bottle away from the kids, so that they do not use it as a toy against the cat. You can also toss the keys toward him, so the noise would startle him. You should get the cat neutered or sprayed preferably at the age of 6-7 months.