Yeah I'm not sure here. At five I knew killing was wrong, and I grew up in a nut farm without any real exposure at all. It is just something innate, I think. You don't have to teach kids not to kill. But whether or not this child realized his actions were harmful, I'm not sure. At five I knew I wasn't supposed to hold my head under water, I knew when my head was under water it was bad, I had enough safety sense to figure that out.
Any parent here would teach their five year old those basic safety skills, and they are smart enough to realize that if it is harmful to them, it is harmful to other people. Children are a lot smarter than we give them credit for. So yes, I think this child must have realized what he was doing was wrong. But, is he fully responsible for his actions? I would say no. A five year old, while smart, does not have the cognitive ability to make life and death decisions like that. Ted Bundy probably saw the knives and thought "Oh man, so cool, let's freak her out!" He probably wasn't making premeditated moves toward murder at five. Do I think he intended to kill the toddler? Nope, because again, rational decision making process not up to par.
God, there are so many contradictions in what I just said. I'm sorry, my thought processes are a mess.
My basic summary is: Five year olds know killing is wrong, and should know drowning is unsafe. Five year olds probably cannot make a premeditated decision to kill that is fully supported like an adult can. So, obviously, he should not be PUNISHED as an adult. Should he be charged? Maybe. If the charge will bring him the help he needs in order to understand his actions, understand their consequences. I'm very sure when this child grows up they will probably have the guilt of the universe on their shoulders, and I think a five year old child can certainly be forgiven for an action they didn't understand the consequence to. There are definitely two victims.