Interesting. We rescued a golden and had him for 5 years. He was the sweetest dog ever, right up until he bit my three year old. Barely nicked him, and the kid did fall onto him while he was sleeping, so we let it go, but watched the interaction between them closely. We figured it was a warning snap, as he was sleeping and it was a natural response.
Then 6 months later he bit him again in the face, barely nicked him- unprovoked. That was enough. Neither time did he turn on him, or really hurt him, but the dog was just not tolerant of a child.
I just wished we had done it the first time. Odd, as I grew up with one and that dog was amazing.
the "labs are harmless, non aggressive dogs" is a bad stereotype. don't get me wrong, i'm not saying they are rampantly aggressive. but they are as prone to biting as any other mutt, german shepherds, and other "dangerous" breeds included. train and treat them like any other breed capable of killing a child.