About 8 years ago mine was in 10U playing in an all day tournament and made it the semi final game. I had got there late as I coached baseball at the time and was warming her up for the game. She played the same team earlier in the day. Coach walked up to me while I was warming her up and asked if she was my daughter " I said yes", he said she needed to work on her leaping but he wasn't going to call it because he had a few kids doing it too. I told him looking right at him to call it or else she is never going to learn... he looked at me like I was crazy but it was more a shot to him to stay in his lane.I'm really late to this discussion, but reading through most of the posts, it got me sucked in. If someone already stated this, then I apologize.
I really hate when an opposing coach has a pre-game discussion about my players. Its like you are trying to stack the deck. I had it happen in HS about my D1 (All-State) pitcher throwing outside the lane. Opposing coach alerted the plate ump before the game. How classy of him! She was never called on it before that game, and never after that game. I brought her in as a relief, and immediately she was called for it. He kept calling it, and try as I might, the damage was done. It got in her head and of course affected the game. That was the outcome the opposing coach had hoped for. Its bush league IMHO. I'm sure the OP wasn't intending to cause an issue like that, but it just isn't cool.
Now, if a kid is quick pitching you and the ump won't stop it, this is a great learning opportunity! The batter can control the tempo of the pitcher. Have your players call time each pitch (look the umpire in the eye when you call time), put one foot in the box, get yourself set, then put your other foot in the box & we are ready to go! No more quick pitching! If the umpire complains about this slowing the game, then state your reason. (i.e "she's quick pitching us blue!"). Don't complain before the game even begins because its an insult to every umpire. My opinion.