Sit facing each other. Clap once, then point at your child so they clap once back.
Keep the rhythm going slowly, one clap each, taking clear turns. Then change the sound — a knee pat, a stamp, a click.
Let your child invent the next sound and copy whatever they choose, exactly.
A clap passed back and forth is turn-taking stripped down to its bare structure, with no toy to want and nothing to lose. Letting the child set the sound moves them from following to leading, which is where the exchange stops being an exercise.