Unless the parents are on the field and quite LITERALLY right beside them. I would not even let them enter the field, let alone hold a gun. If your leader is going to such a d**k about it, then let him find somewhere else to play. You're the one that gets shit on if one of the kids get hurt and you're the one that will get sued. He has absolutely NO say in this.
And even if he does decide to go somewhere else and nobody comes to your field, the field isn't your main source of income nor is it a necessity in your life. Granted it would be a shame to waste all that time into developing a field, all to have some arrogant idiot ruin it for your entire airsoft community.
And waivers aren't very reliable too, unless you're a lawyer and know exactly what to write and what to look for. There are just way too many loopholes that can be used to make you lose in court.