I would be like mom just relax... as long as the kid dont cry alot we wont feed the baby to the snake....lol
Now on a serious note, there is nothing there you have listed that with any common sense would be dangerous (obviously doing something like leaving an adult boa with a child unattended is stupid) I would seriously explain that even as adults the boas wont be eating anything larger than a few pounds, and that the caging is secure. I would also point out the number of people a year killed by dogs or horses every year vs snakes.... I wrote a research paper over the python legislation and came across some statistics cant remember them exactly but over 100 people a year are killed by dogs, and in the last 20 years there have been 8 deaths from constrictor snakes.
And ultimatly if they are not willing to learn or accept it you have to make a decision to have your hobby and tell them to bugger off, or keep them happy and give up on something that you love