When my youngest (my Girl Friends kids) is 10, I will turn 30 shortly after and the oldest will be 12 going on 13. At age 10, they will be ready (if not sooner) to play with the adults and keep up if not out run us all.
As of now, they are 6, 7, and 8. This weekend, we are taking them out to our Teams Field for a game where during the in between time, we let the kids go out (we are right with them helping) with some pumps and target practice on the bunkers. This time will be a special treat as my GF and I are training for Super Game 45 and my GF wants to practice taking cover under fire. So, the kids will be the ones taking turns trying to get mommy in the name of "training".
We hope to sometime soon have a special kids only game with the markers chronoed down so they can finally get to shoot at each other and really have fun. For the time being though, they are still learning how to play and how to be safe.