!!
"All parents will be there. Period!"
While this is a good thing,
do not rely on said parents to supervise the use of the firearm(s) safely/responsibly.
As I'm sure you know, always keep in mind that you (and yours) are going to be held liable for any problems/damages/injuries that may arise. With that said, make sure every parent knows and respects the rules that you set forth and those rules can change. They need to have that baseline level of respect for you.
Whenever anyone gets on my boat, or a boat I am the skipper on, I make perfectly clear everyone knows that what I say is
law - especially those who don't know much/anything about boating or being on the water. This is mostly for their own safety, but more importantly for the safety of others.
I have the firm belief that you may have the unalieable right to hurt yourself, but there is no excuse for hurting anyone else.
I would go so far as to have them sign a contract stating the basic rules of gun handling will be adhered to by all parties involved and the rules (other than the basic concrete standards) can change according to your good judgement. This isn't only to CYA, but to make sure the safety of the kids is insured (often in spite of their parents).
Although I sound like a wet blanket, I certainly think it is a great idea and I wish someone would have thought of the same idea when I was young!!