You need to get a child to understand their actions are wrong. If they know that it is wrong, yet insist on doing it, then you bring in deterrents such as punishment. Smacking your kid or throwing him in the corner for doing something does not get them to understand what's wrong, and if they enjoy doing that particular thing, then they'll just keep doing it while taking their hits.

A lot of the problems with a-holes like the Jersey Shore kids is that they don't look at themselves and say "Oh they dislike me because I get drunk, scream, and throw punches everywhere." They're the by-product of the self-esteem movement that awarded them for doing nothing or outright failing, so they instead think "Oh, they hatin' cause they want my six-pack."

A five-year-old probably doesn't understand drowning as a way of dying (I remember having comic books in school mentioning drowning, but not knowing what it actually meant), and if they do, it's kind of fucked up. Leaving two very young children alone, though, is straight-up negligence. I honestly can't bring myself to ask the babysitter to be punished because she didn't do much beyond living children unattended, and if she's even a half-decent person, having a baby's death on your conscience must be devastating.