Thank you for being a great parent and coming on here to ask us about this.
Slink182 has provided you accurate information.
Something else to keep in mind past the legalities of the matter. Since we are 18+ community enforced, there will be those who ignore the community and allow younger players at games and as a parent you might want to question why an adult would ignore the wishes of the larger community they are supposedly apart of.
Adults will talk about adult things and some of those topics you as a parent of a young teen may not be comfortable. Since this is our time away from our own children, we generally will not censor ourselves.
Put it in another way, you have a weekend away from the kids and are out with friends, think of some of the topics, jokes and behavior you and your friends might engage in away from prying young eyes.
That for many of us is an airsoft game.
Be safe not just with yourself, but those you play with. If you are reckless with other peoples safety then you will leave.