This is the go-to airsoft battlefield for Chiang Mai according to the kids;) Let us know if you've tried elsewhere!
Took a group of 10 year old boys, and they played for 5 hours straight before I had to pull the plug!
Airsoft game for kids and adults
East Chiang Mai, near Promenada Mall
Great place for parents to chill (wifi yes) in their loft lounge area with a good view of the airsoft battlefield below. There was even a proper espresso machine on hand (although we didn't test it out) and a fridge for cold drinks.
Make sure kids wear jeans and long-sleeved sweaters and proper shoes for protection, even in the heat! Price included gear and a small bag of pellets (which was actually enough to last several hours-more for sale on location).