Great post. We need to train our children and even then, there's no way of knowing what they'll get up to when they out with other children.
Also, do we know anything about this neighborhood? Was gang activity common?
The shooter had a wife and child in the house. Perhaps the family inside the house was scared. Perhaps they thought the multiple ringings was a prelude to something more.
Since he had numerous guns, it would be my guess he was practiced in using them. However, we can't know his proficency nor intent. Reports indicate he shot into the ground once, then shot and hit the child. Perhaps he was shooting in the general area, hoping to scare them away. Naturally, he is responsible for where his bullets went - always. But my aim was so bad last time I went to the range, I could never claim to intend harm. From my performance, it would be sheer accident if I hit someone. I'd be firing for effect -- hoping to scare someone enough they'd run away.
I doubt ability was the case with the young man, owner of several guns. Though, perhaps he was just firing in the general direction, without taking aim, and for effect, planning to scare them enough they'd leave him alone. Scare them enough they wouldn't enjoy the game anymore.