You are in charge of a group of fifth-grade children that meets regularly for recreation. Other members of the group have excluded a younger girl and a very shy boy from activities. How could you use reinforcement principles to improve this situation

You are in charge of a group of fifth-grade children that meets regularly for recreation. Other members of the group have excluded a younger girl and a very shy boy from activities. How could you use reinforcement principles to improve this situation? (Include techniques aimed at both the excluded children and the group.)