I think it's important to consider how mature they are as kids as well. It's not just about if they can take getting shot, it's also about whether they're going to be able to be safe whilst playing.
Airsoft guns are toys but they're still more than capable of knocking a tooth our or blinding someone if they're not used responsibly. There was an incident a year or so back of a child who was blinded in one eye when his mate shot him point blank in the face in the safe-zone between games. He didn't realise the gun was loaded, and was only messing around. Since then there have been a lot stricter rules on handling airsoft guns in the safe zones (at least, at any reputable site), but it doesn't change the fact that it was immaturity that led to the incident happening, and it could happen again.
Additionally, I've seen on numerous occasions children negatively affecting the flow of gameplay through either not understanding what's going on, or simply not being mature enough to do it properly. I've seen kids of that age cheating by not accepting their hits, and I'd wager that it's because they're new, so are not doing as well as they'd like, but want to keep shooting at people. So they ignore their hits because they think they can get away with it, and they want to be as good as the people they see on Youtube. I also had an incident(s) last game I played, where someone who couldn't have been much older than 9 or 10 was constantly (literally constantly) shooting people of his own team, and no matter how many times he was told, he didn't seem to understand the concept of armbands and checking your target before you shoot.
In these situations, they might be having a whale of a time, but they're diminishing the experience of others who have paid to be there (whether they realise it or not).
I'm not making any assumptions on the maturity of your kids, nor am I saying that kids shouldn't play. I've only typed that because very occasionally there are instances where I think a kid simply isn't ready for a game like this.
And if they are mature enough that the above won't be any issue, then I'd recommend going with Tackle's idea above, and also feel free to ask here for gun recommendations 😁