I hate to say it, but in our litigious world, you would be held legally liable if a child were hurt on your property. If a kid fell off the porch and were hurt, for instance, the parents could try to sue. I hate to "go there" and talk about the legal aspect but it's very real.
I also think it's slack of parents to let kids run wild. Kids do not learn respect for others' property or personal space if the kids are allowed to roam free. And chasing any animal, pet or wild, indicates a lack of any empathy with how frightened the animal must be. Not a good sign. If they'd caught your cat, would they have returned to gentle play or would they, all juiced up from running and chasing, done something much rougher to kitty?
The parents ought to both keeping their kids on their own property (or at homes of friends or in public space) AND teaching their kids not to touch or chase strange animals, even friendly ones -- that's basic safety, as well as good neighborhood manners. An animal with rabies might seem "friendly" as it raced toward a child when it's anything BUT. Rabid animals often actually approach people rather than fleeing them. A kid used to going right up to animals isn't going to realize that.
I'd definitely contact the parents and in a very friendly way say, "Hey, my cat's really friendly and loves kids, but please ask your children not to approach her if they see her outside. She's loving but I can't guarantee she always wants to be touched. And please ask them to stay out of the flowerbeds and off the porch. I love having kids around the neighborhood but don't want anyone stumbling on the porch or tripping over the shrubs or anythng like that. It's for their safety." And then if it happens again, you'll need to get outside pronto and firmly warn the kids off your porch and flowerbeds and yes, your yard, and I would definitely get pretty loud and firm about chasing my cat! They may say you're the "mean lady" for doing it but your cat will be stressed and frightened if it's chased or even played with when the cat isn't interested. Even the friendliest cat has a right to scratch if it's not in the mood and someone touches it. Believe me, you'd hear about that from the non-supervisory parents.