At their age, sore muscles aren't likely to happen often. I think she's talking about sore joints (she said sore wrists). Kids that age are still developing their joints, and injury like that to them has a greater impact on that development. It's why I never taught joint locks to kids. Extensive punching into the air has questionable value unless one is using it for a specific purpose (stamina development, working on form, etc.), and more so when untrained, and even more so for kids.what children need is plenty of robust exercises not mollycodling I really doubt they are going to be punching the air for an hour, id be surprised if their attention span is five minutes.and if they get tired or bored they will stop And i doubt their punches will look much like punches,And if they get sore arms that's good, that helps them develop,