Pick something your child has a firm opinion about — bedtime, screen limits, which pet is best.
Let them argue their side properly for two minutes while you listen without interrupting.
Then swap: they have to argue the opposite as convincingly as they can. Ask which side was harder and why. That question is the real activity.
Constructing an argument you do not hold requires modelling reasons that are not your own, which is perspective-taking under load. Children who can state the opposing case are measurably better at negotiating rather than escalating.