Players appealing for every decision instead of playing on

I would address it because it affects both behaviour and performance. Appealing while the ball is live usually means the player has mentally left the game for a moment. They are trying to get the decision instead of dealing with what happens next. I’d set one clear team expectation: play until the official stops it. Then praise the response you want. A defender who thinks it is offside but keeps running and deals with the attack has shown excellent discipline. If the appealing becomes constant, I would speak to individual players and, if necessary, use a short substitution as a reset. Competitive football does include frustration and disagreement. Learning to manage that frustration is part of development too. At U13, I would not treat appealing as passion that has to be accepted. The players can care deeply and still stay focused on the next action.