The reason aversive methods or negative re-inforcement should not be used by people who are inexperienced is this. Aversives and negative re-inforcement work because the dog is trying to avoid whatever is going to happen, be that water spray, spray collar, yank on the lead, whatever. The dog views the aversive as unpleasant, whether that is being described as 'suprising' the dog or whatever, the dog doesn't like it, otherwise it wouldn't work. Some inexperienced and who doesn't fully understand canince body language could easily mis-interpret the dogs reasons for behaving in a certain way, or get the timing wrong. For example, if you're using a spray collar, (which has been mentioned on thsi thread) and your dog happens ot be noticing your child in the second you spray it, especially if this inadvertantly happened more than once, which is a distinct possibility, then the dog coudl associate the unpleasant experience witht he child an dthen develop a strong dislike to the child, possibly even escalating, depending on the aversive used, how the dog views the aversive and what the dogs original reason for the unwanted behaviour was, to attacking the child. So, something that could have been easily handled turns into a nightmare situation.

I have never heard of anyone suggesting using a water spray for normal puppy biting, it simply isn't neccessary, let alone a good idea.

There are lots of experienced dog owners, breeders and trainers on this thread, and only one of them is suggesting a water spray, doesn't that tell you something?