5 Hula Hoops.
Audience response decides winners.
Choose the group that should go first, boys or girls. Each group has approx. The duration of a short but fast song is sufficient, e.g. Hippie Hippie shake. There should be two winners, one from each group, unless you decide a play-off would work. Some form of bribery is always the key to this comp, offer each of the contestants something token as a condition that they agree to do anything you ask.