I can't recall a serious incident either. These snakes are not large constrictors. Most max out at 5 feet or less. The max size prey a ball can probably kill is a large rat size equivalent. I've been bitten a few times but they were not out of aggression. The snake was being defensive when I accidentally startled it. The bite didn't hurt. Felt less painful than a pin prick from the doctor.
All you can do is educate your family and show them that the snakes are in a secure enclosure. There's a reason why Ball Pythons are a beginner pet due to their docile nature. The bad stories you hear about a snake killing a child are usually larger species that escaped an ill suited enclosure that wasn't secure. For example, adult boas or burms kept in screen top tanks. And even those incidents are very rare. I hate to use this example, but family dogs kill ~20+ children a year on average. The point I'm trying to make is that people underestimate some animals and overestimate others....(Aaron beat me with this example!)
Good luck.
Sent from my DROID RAZR using Tapatalk 2