OK thanks Mid.
So, these are the things that come to mind..
I wouldn't bring it up prematurely. If this player "could easily see V innings...", that doesn't necessarily equate to him throwing a lot or taking a heavy load that first freshman year. I would give it at least a little time for the player to settle into the program and maybe see where he stands and what guidelines (if any) the coach shares directly or what is observed with other P's in regards to pitch counts. Also, make sure player/parent knows specifics with regulations specific to age/grade in the state he plays in. Are the counts less for freshmen than for upperclassmen? Are those guidelines sufficient to satisfy the concerns of the parents?
If, after figuring things out first hand, they still feel they must address concerns, I think these are the keys...
Pick the right time and place to talk to HC. Ask for a few minutes in private.
If, when talking to the coach, the parent first shows appreciation, support and respect, the HC should be much more open to mutual discussion. The parent should also assure the HC that he will always let son handle his own business with the coach except for those few issues where parents have to be involved. Assure the HC that you will always support the team, the program and his coaching decisions and will never be that problem parent. Let him know that the only time you would ever speak up or raise a concern would be with any safety/health issues. And being a parent of a young pitcher, that is particularly challenging for you. Show appreciation that player has the opportunity to be a key pitcher for the team. Share that son would never bring up this concern because he only wants to be a good team player and do whatever coach and team need him to do. Share that you have done a good deal of research into proper pitch counts for a pitcher that age and you were hoping to compare notes and gain a better understanding of what the coach uses as guidelines. Be open to a different perspective and ask questions if his guidelines differ from yours.
If things are presented this way, the coach should be very aware of your concerns and expectations in regard to proper care of the health of son's arm. If any issue arises after that, the groundwork has been laid to take whatever action is necessary.
For myself, as a HS coach, I am very insistent that the HS sports experience includes the direction of the HS athlete handling things themselves. But, as is discussed often here, safety and health are the exceptions (of course, as would any type of abuse). So, if a parent handles things in a respectful manner, I have no issue addressing those concerns and working to a satisfactory resolution. Most other coaches, I believe, are of the same mindset.