Long post Melissa, but you asked for an explanation so here goes.
If a dog is handled properly from the beginning, he is very very unlikely to bite a hand of a child. If he is properly socialized to children, if he is treated kindly by children and by all and pleasantness is all that is associated with children during and after his critical socialization period, it is very unlikely that he will bite a child. He will learn tolerance and acceptance of people of all ages around his food and tolerance for accidents that happen such as getting a foot stepped on or an ear poked. He learns tolerance as a pup because he learns that bad things don't happen in association with people; adults or children. My Doberman got stepped on, tripped over, run into by various people and he just looked like, "duh...what happened?" That's because he knew no one did anything on purpose. It had not been a part of his repertoire growing up.
If a dog does bite a child due to poor training and handling, that behavior can still be modified. If it happens "out of the blue" (which is a crock anyhow....things like that don't happen out of the blue. There's a reason for it) then you have to interrupt things so it doesn't continue or happen again. You have to do what you have to do to make the child safe at that moment.
However, that moment, that emergency is NOT the time to train the dog about not biting children. That is NOT the lesson time. A desensatization process or program needs to be implimented whereby, there is adequate flight distance between the dog and the "bad" thing....children in this case. To simplify: the dog must be made to believe that the child is not a threat, not a scary thing (if that is the reason) or not prey (if that is the reason). In other words, the child must be made into a good thing, a thing that is to be trusted and that the association therewith is nothing but good things, things the dog wants and likes. Child equals
fantastic. This is a bit of a short version, but the concept is just that. Causing the dog fear and pain, as in harsh correction associates the child with a rotten time. Child equals bad. Dogs learn by association. If you supress the behavior, supress the bite or growl (those are communication) you do not supress the underlying reason the dog bit in the first place. You only supress the bite behavior. So, he may not bite for a long time to come. But because the child is still not a good thing, it is very common for this kind of behavior to regress as in the expression, "ticking time bomb." It can come out later in an explosion. And it does very often. This is documented by many reputable, well known trainers, not just my opinion or experience.
Punishing a dog for a behavior which is normal for a dog without teaching an alternative and a way to deal with the actual issue is counter productive and wrong. Biting is normal dog behavior. It isn't normal for us and doesn't fit into our culture or society. But dogs don't know this in a moral sense. So, when you hit a dog or "correct" him sternly for something that is in his communication system, you are only shutting down the communication, nothing more. And that is dangerous and unfair......and not the way dogs understand things.
Why not learn to train in a way that dogs can relate to based on their natural ways of learning? When you go to a foreign country where people don't speak your language, do you talk to them in your language only and expect them to understand? Or do you try to use some of their language and maybe some hand signals or drawing something on paper....something that they can understand so that you two can communicate?
It's the same with dogs. Show the dog what you mean in a way he can understand your language and try to understand what he is trying to tell you. Dogs have a rich array of body and facial signals which mean different things. People have studied this for a long time and observed and experimented with. And there are signals and social cues that we use that they can understand....there are some. But not everything we do translates into something they can understand.
THAT is why learning canine behavior is so important, not learning by only your interpretation, but taking in what others have learned before you, studied, experiemented on, had success with, gone to universities for advanced degrees in behavior, trained many many animals.
There is more than scolding a dog when he doesn't perform a behavior to your liking. There are ways to get him to perform to your liking without hitting him....ways which coincide with behavior law, proven concepts and techniques...Behavioral law is like a law of physics. Apples fall off trees due to gravity. Dogs learn by reinforcment due to behavioral law. Dogs are not obedient to cues and commands. They are obedient to behavioral law....something that is falling on deaf ears here.
The training "methods" that are what you advocate are not responsible training. I am sorry to be so blunt. But training by means of force and supression, submission just isn't nice and does not make a dog happy. Wagging tails are calming signals in the case of dogs who are so harsly treated.
My Doberman is very obedient, very well mannered, trained in a few venues, very well socialized....is a dream dog. I never laid a hand on him. The most I've done is tell him strictly, "eh-eh!" Or sometimes "NO!" Or even sometimes, "knock it off!" I have never stomped toward him, intimidated him. He has been trained completely with motivation and reward. If there is a behavior problem that has cropped up, it was dealt with, not in a direct approach, as in right then and there. But after, as a process. For example, he got snarky with my male Chihuahua for a brief period. I think he was getting possessive of me a little bit. So, when he looked like he was about to bite Jose`, I hollered, yessireeeee! I sounded vicious! "NOOOOO!" And I stepped in there and pointed my finger out the door...."OUT!" Yes, I was scared. Jose` is a little dog. So, no...that was not the best way to handle it. That was not the way to train Lyric. That was the primate in me....waving, failing arms, loud screeching noises like a chimpanzee. It taught Lyric nothing. If anything it made him associate a rotten time in close proximatey to Jose`...not a good thing. So, from then on, I decided to impliment a more ridgid NILIF for a while and I was very careful with Jose`. Lyric did this snarling routine a few more times and each time I calmly told him "out" which means out of the den. I put him in my room alone and closed the door for a few mintues. I then kept Lyric out of the den (where this problem happened, and only there) for a couple of weeks. No longer was he allowed to hang with me very much. I was aloof. Then I let Lyric back in the den with Jose safely tucked under a chair where Lyric would have a hard time getting him, if he were to snarl or snap. Lyric would lie nicely rather near the chair and mind his own business. He got tiny terats dropped for him and lots of love. Those nice things were happening in the presence of Jose`. "Oh wow....look at this.....when Jose is around, good things happen." It was at least 6 or 8 months and I never had a single incident again. I no longer give treats as much, although I still do randomly while they're both in the den with me. So, the payoff for his good behavior is treats and he gets to be with me in the den. And Jose turns into a pretty good thing to Lyric. It is in association with him that he gets good things. Behavioral law: when there is a payoff for a behavior, that behavior is much more likely to be repeated. When there is NO payoff for a behavior, that behavior is much, much more likely to extinguish.