Do you warm up pitchers?

I would agree that a coach should try to give guys more heads up in games that they may be coming in to pitch. But me thinking that doesn't mean your coach is going to change anything, so I would suggest to your son that if he thinks he may come in to pitch to head down to the bullpen between innings to start getting loose. Obviously he needs to be mindful of where the team is at in the batting order, but that would help. I've even seen outfielders that may be coming in to pitch get their partner that they throw with between innings squat down like a catcher and they'll get in a few tosses that way between innings. Find a way to improvise rather than using the coach as a crutch.

What I've done in the past and what we do at the school im an asst at now is basically the same. I would tell the pitcher who's going to start at least the day before he was the starter. This way if he wants to do whatever it takes to get ready he can be ready. If he's a guy that can show up and be told he was starting and be fine then no big deal. Typically guys will figure out who will be pitching against who and already know - when this happens it allows them handle surprises if need be. One time I told a guy he was starting the next day and that night his parents kicked him out of the house. I told him to not go to the game and take care of things at home and just bumped up the next guy who had a pretty long rest. He knew it would be him who was going to get moved up so he was ready.

As for pitching changes you have to do everything in your power to allow them time to get loose before stepping onto the mound for their 8 pitches. Sometimes that doesn't happen but if you're doing your job then you can be prepared.

We watch the pitch counts, effort and effectiveness of the guy on the mound. Once he starts to get into the area of high pitches, more effort and / or struggling we get somebody up immediately if he's on the bench. I take them to the bullpen and try to tell them about the situation they will be in. I make them get loose from the set position because it's quicker and probably be the situation they will be going into. Once they are warm and ready they can go from the windup. Plus we try to get into a rythem with the guy in the game. We will watch his pitch and see what happens. Then the guy in the bullpen will throw his. Watch the pitch on the field and then throw the bullpen. Helps with the rythem of the game.

If they are in the field we have a catcher ready and the second they come in from the field they head straight to the bullpen. Once there we try to go as fast as we can without possibly causing an injury. I tell them to get close so that if they go in they can get there in the 8 pitches they get. This way they don't get all the way warm and then cool down.

If they are up to hit and can't go to the bullpen we will have them basically throw a flat ground with the first baseman (or other IF) when we go back into the field for warm ups. For example we want to bring our SS into pitch eventually. He and the first baseman will throw with each other. The SS will just throw hard to try and get loose. He doesn't throw pitches or really mechanics outside of get into balance position and go from there. The 2B and 3B will throw with each other to give them something to do. It's not the best way to do it but for the situation it's better than not throwing at all and then getting onto the mound for 8 pitches.

That is common for many 13U/14U travel teams. Not right, but common. The starter needs to be ready. Someone needs to have a chat with coach about the lack of warmup time for relievers - it's an injury issue.

There are times when the starter is cruising and then he just loses it and the pitcher you want to bring in is at a position and yes, he only gets the eight warmup pitches. I do tell my pitchers before the day of the game who is getting the ball and I often give the guy I know will be first in relief a heads up too. This is a legitimate question, but it almost reminds me of the parent who in my first year of coaching (summer of 2007), asked me why I did not warm up two pitchers in the pen before a game.

This is unfortunate that it happens. It happened to me often even in High School. Most of the time I started, however, I was called to relieve in between starts often.
What worked better for me if I was given a couple minutes before I had to be on the mound was running to the fence and back first. You want to get the blood going first. Warm up to throw; don't throw to warm up.
You really throw with your legs and hips, so I would hurry and jog to the fence if time permitted and then threw my 8 throws.
I did have it good though because after someone was struggling I figured I was going in so I would always be jumping around the dugout, doing elastic band work etc while cheering on the team. I just always assumed I would go in; I think all pitchers should assume the same.
Good luck!

Normally I like to tell my starter before the game. I also like to give a heads up to at least two or three other guys and let them know they might be coming in. That way it's not a surprise for that player later in the game.

I tend to pay attention to mechanics, as I know when my guys are starting to tire. However, it IS baseball, so anything can happen.

Usually I will tend to have a kid on the bench, or make a defensive replacement during an inning if I have to, so a player can warm up before coming in the game.

A lot of coaches (especially little league rather than high school) do as your son's coach does. I can understand not telling relievers, because at that age, many pitchers are also position players, and the coach doesn't know in advance what inning he will pull the starter. At that point, your son should be warmed up from playing his position plus the limited amount of warm up pitches you get that he should be fine. The coach should definitely tell the starter the minute he arrives at the field that he will be starting. Some players prepare differently when they know they are pitching. Just tell your son to talk to the coach and let him know that he would appreciate some warning if possible before he is called to pitch. It should be as simple as that. Cheers!