Unleashed dogs?

What do people think of unleashed dogs in public? My partner and i took our 4 and 6 year old children to the lake and park. Then out of nowhere came this dog that proceeded to jump at them and go crazy. They have had a couple of bad experiences with dogs so they were petrified. The owner of the dog made it out to be our fault as the kids were scared of dogs. I have taught them that no matter how tame a dog looks do not touch it as dogs can bite. We actually checked that the area wasnt a leash free area before deciding to go there. I know people should be able to take their dogs out but why not take them where they can go leash free. This park actually had a childrens playground so they mustve been aware there were children around. I think its great people having animals but shouldnt there be responsibilty that goes with it?