How are you briefing parents before 3v3 starts?

I’d explain the reason before you explain the rules. If parents only hear “please don’t shout instructions”, some will feel like you are asking them not to support their child. I’d tell them that 3v3 is giving the children more chances to make their own decisions, and that the coaches are deliberately going to step back as well. I’d keep the message very practical: encourage them, celebrate effort, enjoy the goals, but try not to tell them what to do with the ball. A short meeting or message before the first matchday is much better than trying to correct people while the game is happening. And I’d include the coaches in the same promise. It lands better if parents can see that the adults on both sides are also resisting the urge to control every moment.