my 2 cents: i do think that a full grown alligator gar has the capacity to eat a kid (whether it would or not is another matter). Judging by the size difference, i would definitely agree with the point of view that it will at least check out the splashing in the water and eye the kid who does the splashing.
My gar has bittern gardener's finger after he wiggled it in the water (blood was drawn, but gar retreated once the hand was snatched back). I am not entirely comfortable with sticking my hand (for whatever reason) into the set-up with my now-rather large gar (one of the reason i do not feed my RTC with my hand cos gar lurks around lol). I would definitely not go into a pond that has a 6' gars in it - i am certain that 6' gars in the pond WILL eat a kid if they are hungry enough (and have not been pellet trained)