Should I use a leash on my cat?

I had three kittens that I got from the dumpster too, and so I'd let them out and run around for a little bit outside, then they'd come back home, until one of the kittens got hit by a car - I was devastated. So now, whenever I feel like letting them out for a little fresh air, I put them on a leash and let them wander around. So I suppose you can try to leash them, but use a harness, not a collar - they'll slip out of it too easily, and probably be mad at you for the leash thing nonetheless. Just wander around with them around the yard for a bit, if you want, on a longer leash, and that would be a good solution for it. But I would tell the police if that child does that again - that's animal cruelty and against the law.