Simple. On a paper plate or sheet of paper make a 6" diameter circle, with a pinpoint mark at the center. Shoot 3 arrows, seated or kneeling from 12 yards (6 got kids). For tiebreaker, measure closest one to center from nearest part of shaft to middle of pinpoint.
Winner will have the most arrows in circle (cutting or touching line counts as "in"), with closest arrow to center point for tie breaker.