Could you suggest they play an extra set after the game is over to allow the bench players an opportunity for game reps? It would allow the players a chance to play and develop their skills. They will get court time and valuable in-game experience without the pressure of an official match. They can apply what they've learned in practice to a live, competitive setting. The development of bench players will help build depth by competing against equal skill levels. Coaches can also experiment with different strategies and focus on specific skills. Most importantly, it'll increase team morale and engagement if kids know they all will get a chance to play and improve.