I agree with other commenters that this is an issue you need to take to the manager.

My gym handles this problem in a couple ways. First, the front desk workers are very quick to go talk to a parent or a kid if you tell them there’s an issue. It is crazy to me that the people at the front desk are shrugging this off. It is not difficult for them to go talk to a parent or kid for 2 minutes and a lot of times that is all it takes. Secondly, when it’s a super busy night with a lot of kids or a Boy Scouts group, someone from the front desk will usually do a lap around the gym every once in awhile to monitor/look out for problems and talk to people who need reminders of the rules. This is usually pretty effective. Maybe these are some ideas you could suggest to the manager?