Oscar, four and a half, and his little sister Alice, two, were rolling around on the living-room rug, trying to catch each other’s feet.

Alice was squealing. Oscar was laughing. One of the sofa cushions had already hit the floor.

Julien, their dad, had the words ready: “Stop, no more fighting.”

Then Alice shouted, “Stop!”

Oscar stopped straight away and moved back.

Two seconds later, Alice threw herself at him, shouting, “Again!”

Julien kept an eye on them, but he didn’t interrupt the game after all.

When children play-fight, the noise, rolling bodies and shouts can look exactly like the sort of thing we normally step in to stop. But that evening, something mattered more than the volume: both children were still in the game, and Alice’s “stop” had worked.

Play-fighting or a real fight?

Julien started watching something other than the commotion.

Oscar and Alice both came back to the game. They were laughing. Sometimes Oscar chased Alice, then she jumped on him. Most of all, when one of them moved away or said stop, the other slowed down.

That didn’t mean the living room had no rules. Alice was two and Oscar was four and a half; the difference in size and strength was reason enough for Julien to stay close. A game can tip over, a child can get carried away, and someone who was laughing ten seconds earlier may suddenly stop enjoying it.

The point wasn’t to “leave them to it”. It was not to stop physical play automatically just because it looked wild.

The rule that matters: anyone can stop

This kind of play means constantly reading the other person’s reactions: too hard, not hard enough, again, stop.

To keep it playful, Julien eventually set two simple rules:

“You can carry on only if you both want to.”

“When someone says stop, everyone stops straight away.”

If one child cries, tries to get away, can no longer say stop, or the other carries on despite a refusal, an adult steps in. Laughter doesn’t mean anything goes, and “stop” doesn’t have to be perfectly phrased to count.

A few minutes later, Alice shouted “stop” again. Oscar froze. She put her sock back on, got up and charged at him.

Julien hadn’t stopped watching the game. He had simply stopped confusing noise with danger.