Yelling at the parents is understandable given that you just potentially just risked your own life to save the kid of inattentive parents, but if concerned as to why your did it, might consider why you didn't yell at the parents of the other 3 kids, or the adult that you saved, were these parents just less appreciative then the others?
I would have likely scolded all of them, including the adult, for being dumbasses.
Naw, I just make sure they're breathing and able to move on their own and then walk away. Not even sure why I did it. Knee jerk actions really.