Do you let U13s decide their own set-piece takers?

I would let the players have a strong say, with the coach setting a few boundaries. Set-piece responsibility can be a useful confidence and leadership opportunity at U13, but leaving everything to “who grabs the ball first” can create arguments or the same dominant players taking everything. You might agree a small group of players who are comfortable taking corners, free kicks or penalties, then let them decide within that group depending on the game. I’d also give other players opportunities in training. The key is that the responsibility should not become a status symbol. A player who misses a penalty or takes a poor corner should not feel they have lost the role forever. At this age, shared ownership is useful. The coach can create the structure, then give the players room to manage it respectfully.