The game a child invents deserves a chance before an adult improves its rules.

Invented games look broken to an adult because they are measured against fairness, balance and a clear ending. That is not what they are for. A child making up rules is practising invention, negotiation and the pleasure of authorship, and an adult improving the design takes over the one part that mattered.

When a child explains a game they made, play it as written, including the parts that make no sense. Ask a question about the rules rather than fixing them. If it collapses, let them be the one to change it.