The games are played for the kids. Remember that point. Children are very aware of fairness and respect. Play everyone and play them equally, showing that just because some are more gifted or advanced, they are not more special or important than the rest of the team members. When you allow everyone to try a position and play equal amounts of time, more than success through a winning score is developed.
Children learn what it is to be a member of a team.
Allow the children to help evaluate their position on the team and their performance level. It gives them a sense of responsibility and ownership over their development and goals. Recognize when a child is struggling and then offer support. Let the child suggest what changes could be made. Sincerity is crucial.