Dad was with the boy, according to the story, 10 feet away and getting his camera out to take a picture. It also says he thought the smaller Uzi would be a safer weapon for the boy and was assured this was so by someone present.
Dad was not charged because it was felt he couldn't be expected to know as much as the people presented as experts.
I can’t believe they thought it was safer because it was smaller. Recoil is inversely proportional to mass, you idiots! This micro-Uzi thing is so light and has such a high cyclic rate that it’s hard to think of a gun that would be more dangerous for an inexperienced kid to fire. He’d have been fine shooting a big heavy SMG like a Tommy gun.