Unfortunately, children comprise 60% of the dog bite victims.
Children often makes dogs nervous, because they do not behave like adult people. In fact, some dogs don't even recognize children to be the same species as adults. This is because children smell differently, move differently, sound differently, and are shaped differently than adults. Children also tend to portray many “rude” behaviors toward dogs. These include things like approaching rudely (running up to a dog suddenly, and walking straight toward a dog while staring and making hard eye contact), looming over and petting the dogs' head, pulling fur, pulling tails, climbing the dog, making faces, barking, throwing things at the dog, biting the dog...etc.
This can all be quite overwhelming for a dog who hasn't been around children a lot and hasn't learned to put up with these behaviors. Most dogs will give many warning signs before actually nipping. These warning signs can include whale eye (the white edges of your dogs' eyes will show more prominently...appearing much like crescent moons), panting, drooling, turning away/moving away repeatedly, excessive licking, shaking off, or scratching, freezing, lip curls (showing teeth) and growling.
NEVER correct your dog for signaling that they're stressed or overwhelmed. At best, this teaches the dog that their warnings are not being respected and they need to go straight to biting to get their message across. At worst, the dog thinks their warning signals aren't working AND that the correction has something to do with the child being nearby. This can actually cause them to become even more anxious and even aggressive around children.
If you notice these warning signals, calmly, but quickly, move the child away from the dog, or redirect your dog over to you. Do not pull on your dog (or the leash or collar), because this can be seen as a correction and the dog might associate it incorrectly with the child. Give your dog a break and some space away from the child. I cannot stress this enough – Do not hesitate to correct a child or their parent if they continue to push your dog after you've asked them not to! Too many children are bit, and dogs put down because parents don't take a dogs' warning signals seriously and think their childs' rude behavior is cute.
Instead, find your dogs' threshold – the point at which your dog is aware of the stimulus that creates anxiety or aggression, but they can still listen to you and perform known cues. This might be 10 feet or 200 feet. Each dog is different. I recommend starting about 50 feet away and moving in closer or farther, depending on your dogs' needs. Parks and bus routes are great places to work with your dog if you cannot find willing friends and family with children to work with you. If you do this though, make it very clear you are training your dog and don't be afraid to tell children your dog isn't friendly and that you both need space.
Beginning with high-value treats (like hot dogs, chicken or canned cat food), reward your dog each time they look at the children, then back to you. If your dog isn't looking to you on their own, make a few encouraging noises (kissy sounds) or call your dogs' name to encourage them to look back to you. Reward them for doing so. If you cannot get your dogs' attention, you're too close and need to increase your distance from the children. Try again until your dog will willingly look or move toward the children, then look or move back to you. This teaches your dog that each time they pay attention to the children without reacting, while remaining calm, they get lots of yummy treats and praise. They'll begin to think that maybe children aren't such a bad thing after all. As your dog becomes more comfortable with this exercise, you can gradually move closer. Eventually you will get to the point where your dog is comfortable being next to children, without being touched. At this point, you can ask willing children to help you by walking by your dog and tossing them treats. Once your dog is comfortable with this, you can do brief meetings between your dog and children. Ask the child to pet your dog calmly, under the chin, on the dogs' chest, or below the shoulders. These are places most dogs find less threatening to touch. Ask the child to give your dog treats and then walk away. These first meetings should be less than five seconds.
Again, as your dog becomes more comfortable, you can increase the meeting/petting times. If your dog loves to chase balls or play tug, enlist a child to help you play with your dog. The goal is to teach your dog that children being around means lots of good things happen.
If you are in the process of working with your dog around children and a child comes into your home (with friends or family), make sure your dog has a place they can escape to without being bothered. A dog bed, a crate or under a table are some good options. Make sure your dog understands that while they are in their “safe place” you will make sure the child doesn't bother them. If you cannot supervise your dog with children around, physically separate them. Do not set your dog up to fail or the child to get hurt. Be sure to watch your dogs' body language for signs of stress.
If your dog backslides, which can happen (dogs have good days and bad days, just like people), don't get discouraged. Simply go back a few training steps and work your way forward again. If you are having trouble with these exercises, please talk to your trainer. You may want to consider private training sessions with a trainer that has experience working with reactive or anxious dogs.