I would say something, calmly and early.
An opposition coach should not be coaching your players. Even if the advice is harmless, your children should not have to work out which adult voice they are supposed to follow.
I’d speak directly to the coach at a stoppage: “Can you leave our players to us please? They’re starting to respond to your instructions.”
Keep it factual and avoid turning it into a touchline argument.
If it continues, involve the match official or the appropriate organiser rather than shouting across the pitch.
I would also reassure your players beforehand if it has become a pattern: listen to your teammates and your own coaches; you do not need to respond to instructions from the other side.
This is one of those adult problems that children should not be asked to solve for us.
