Does every U7 mistake need a coaching point?

No. Most mistakes need another chance, not another speech. One of the big strengths of 3v3 is that the same player may get another similar moment very quickly. A poor first touch can be followed by another first touch. A bad pass can be followed by another decision. I’d intervene when there is something important the child is unlikely to solve alone, a safety issue, or a repeated picture you want the whole group to notice. Otherwise, save it. You can also keep notes for training. If you see the same receiving problem across the morning, that might become Tuesday’s practice instead of Saturday’s fourth mini-team-talk. The coach does not have to prove they noticed the mistake by commenting on it.