Although I agree that kids shouldn't be running around in a dog park, your dog's behavior could end up in a nasty lawsuit. If I had a 140 pound dog and little kids were running in the dog park, I would not let my dog loose especially if I knew he liked to chase and "mouth" children. Even if he just liked to bump them, that is not appropriate behavior. What if he "bumps" an 80 year old lady and she breaks her hip?