A made-up game can give a child practice in asking, agreeing, and trying again.

Invented games are negotiations wearing a costume. Before anyone plays, the children have to propose rules, argue about them, settle on a version everyone accepts, and repair it when it stops working halfway through. That is a lot of social machinery running under what looks like nonsense with a stick. Adults sometimes rush to organize the play and accidentally remove the part doing the most good.

When children are making up something chaotic, hold off on improving it. Answer questions if asked, and otherwise let the rule arguments happen. If you join in, take a part rather than the position of judge.