What would you do? ( beach etiquette )

You’re at the beach, you don’t have any kids with you but there are a bunch of kids in the area you’re in. You see one group building sand castles near u and another playing in the tide.

The sand castle group runs to the water to get water for their “moat” while they’re in the water, the group of kids that was playing in the tide comes and stomps the sand castles to the ground.

This happens a good 2/3 times before the sand castle group speaks up, but the tide group is persistent and continues the destruction.

Do you step in? Or do u just let the kids play?

Bonus question:

Would your reaction be any different if your kids were part of either group?

We’re the kids from the tide in the wrong or is everything fair game at the beach?