I believe maybe the father was not that experienced with the use of firearms. The first thing he should have did when he brought those young kids out their was explain muzzle awareness, range rules and common courtesies on the range, recognizing dangers and calling seize fire. Explaining the function of each weapon that they were firing and how to perform S.P.O.R.TS. on a weapon that is malfunctioning. That is the basics. I will be taking out my neighbor’s kids who are 2 teenagers to the range to fire a rifle for the first time. I have an AR-15, I do plan on giving them a full Military style breakdown on safety, how an AR works, zeroing, how to take it apart, what to do when you have a malfunction the entire bit. Range safety is important! Like you said if he had a lot of kids (More than 2) with him it would be best to do that before getting on to the range and also he should be watching them closely to make sure they are not committing any us-safe acts. Storm Trooper I commend you because if I was there I might have went up to the father and said something to him especially if I felt unsafe.
"Better to fight for something than live for nothing."-General George S. Patton
"He said to them, "But now if you have a purse, take it, and also a bag; and "if you don't have a sword, sell your cloak and buyone.'' Luke 22:36