I agree that as a dog owner, it is your responsibility to police the public, including children. It shouldn't be, and it isn't fair, but it is the way it is. You cannot rely on strangers to be sensible, and your responsibility is to keep your dog safe and keep things that it is afraid of, or that could hurt or startle it, at a safe distance.
I understand it's not easy. One of DD's chihuahuas is gorgeous. He is, without bias, the cutest dog you will ever set eyes on. He is also the canine embodiment of pure evil. What started as fear aggression ended as attention-seeking behaviour; he knows if he growls, snarls, or snaps at strangers, someone is likely to pick him up and hug him to remove his ability to bite the object of his rage.
Walking him during the summer holidays is hell. He is a child magnet. He also loves nothing more than causing fear and misery, and children are his preferred targets, not because he's scared of them, but because he knows he is more likely to be picked up to keep the children safe from his wrath. Parents think his warnings (snarling and growling) are funny and cute. They don't often warn their kids to stay away, no matter how much we beg them to.
As much as I'm tempted to let him bite people who intrude on his space, I don't, because I am responsible for keeping him safe, and that means not allowing the targets of his hatred to get close enough to him to be bitten.