Deputy acted accordingly whether the child was there or not!
Some lunatic charges you and closing fast and screaming a war cry of obscenities with a raised weapon in hand leaves you NO TIME to second guess things or probably even try to move off axis. Especially if he had his back to the threat initially or was kneeling down talking to the boy at the time of the attack.
Doesn't matter whether the weapon was a rifle, table leg, piece of rebar or for that matter a woofle bat.
It's in the dark, the man is running directly at you screaming waving what appears to be a weapon.
This is what you call "The Moment of Truth" and a time for a life or death split second decision.
Whether the child was there or not, if the deputy hesitated he very well could have been dead. Permanently!
Good shoot as far as I'm concerned!
I have seen LEO's use incredible amounts of restraint in order not to shoot someone who they were within their legal right to do so based on Ability, Opportunity and Jeopardy and end up making an arrest instead. It's a dangerous gamble every time they do that, but they do it because no one who is good, rightous and moral, really wants to kill someone. In this case, I believe the deputy had no choice!