I would start by matching the adults' reaction to the size of the problem.
One poor U11 performance is not evidence that the formation is wrong, the players need more training or the group is suddenly not good enough. Sometimes children simply have a poor game.
I would review it calmly and look for repeated patterns. If something has been happening for several weeks, it may deserve attention in training. If it appeared once on a difficult Saturday, I would be very careful about building a big response around it.
The fact the children had already moved on is important too. Adults can accidentally give a bad performance far more emotional weight than the players themselves.
A simple message to parents can help: we will review the game, take anything useful from it and continue with the longer-term development plan.
At U11, perspective is part of the environment adults create.
One bad match should remain one bad match, not become a verdict on the team.
