Wow some of these stories make me nervous! The open gym where I train is the same as 'Adult Rec' and 'Teen Drop-in', there is no open gym for young kids. Adult Rec is 18+ and there are usually 20-30 people there with 2 or 3 coaches. Most of these people do parkour, some do gymnastics and ocassionally there are some retired elite/national gymasts and cheerleaders. I imagine the Teen drop-in is a bit more chaotic because the kids are 13-17 and less observant of their surroundings and less competent in their skills, but there's still enough coaches to go around and everyone has to sign a waiver. In both situations there are people who try skills way beyond their level and if the coaches don't catch it in time can have some pretty scary falls, but there have been remarkably few injuries. I don't think my gym would ever allow open gym for young kids and their parents, as a lot of parents have no clue about safety in the gym (like don't trip and fall into the pit, don't cross the floor when people are tumbling, uneven surfaces, etc).