Don't be nasty. In any case, it is the owner's responsibility to maintain control over the dog at all times and to also control any interaction between the dog and other people or animals. There are a few common sense rules that any dog owner should follow:
Don't allow anyone to approach your dog without asking, whether it is a child or an adult. This allows the owner to get control of the dog, to assess the dog's body language and to let the other person know the proper way to approach the dog. You should know your dog much better than them.
If out on a leash, shorten the leash or put the dog in a sit. A properly trained dog will be less likely to make an unexpected move while in a controlled position.
Never let the dog approach a small child. They are more likely to show fear or stick their face in the dog's face, either action leading to a possible bite. It is not the child's fault. Similarly, never let the dog approach anyone who is afraid of dogs, just to show them "there is nothing to fear". At home, you should not leave a dog alone with a small child.
You should not let the dog off leash, especially when there are people, wildlife or other animals around. Even the best trained dog can be unpredictable in a given scenario. Do everything possible to keep the dog from getting loose from your home, yard or campsite.
Always practice "defensive dog handling". In any situation, you should assume the worst case, and be prepared. Your dog is your responsibility, noone else's.