(not to sound like a smart...) What happens when a lil child (1yr old) commits murder? [ex. parents sleeping and child sets house on fire]

One of the necessary requirements to be convicted of murder in Arizona is to have the intent to kill someone else. You must at least know or be aware that your actions will cause, or will likely cause, the death of another. Having some knowledge of one kind or another of what you're doing is necessary to be convicted of any crime. So a one-year-old child will likely not be convicted of murder, or any other criminal offense, because they likely don't understand what they're doing, and the law will not hold them criminally responsible for their actions.