What are you doing with handball in 3v3?

I would keep this very simple and, importantly, check whatever guidance your league or County FA is using for the detail. The national 3v3 summary sets out the main format rules, but it does not spell out a separate handball interpretation on that page. So I would not invent a local rule and present it as official. For the children, the facilitator should be helping the game move rather than looking for every accidental contact. If a child clearly picks the ball up or deliberately handles it, deal with it quickly and restart. If the ball simply brushes an arm in a crowded U7 game, I would be very wary of turning that into a debate. Most importantly, get the adults on all pitches using the same approach.