Well the positive (I'm assuming) is that you're on here venting and saying what's going through your head because if you took this to the coach it may not end well. Honestly there is nothing to complain or question as to what's going on with your son. He's in the lineup, playing, contributing and helping the team win. It's on been a handful of games, he's a freshman and it's freshman ball. He will get his due if he's good enough. As cabbagedad said - frosh and JV is about development and sometimes it's tough to get enough innings for everyone to see how good they are. Practice is a wonderful place to learn the game and get better. It is supremely vital to the development of a player to learn and produce in practice but where you figure out if you're a player or not is in the game. There's a reason why the phrase "play yourself out of the lineup" exists - a coach uses a develepmental level team to figure out who is going to be there in 4 years helping to produce. Those 16 kids on the frosh team will not all be on the varsity team in four years. My guess is that at least half will be gone by then, if not more.
Relax, take a deep breath and enjoy what you're son is doing. Provide guidance and support for your son because he will face tough times in this game. He will need someone to help pick him up and not turn him into a victim when he's not in the lineup.
Always remember - it's best to be on the field at your secondary position than to be the number one back up at your primary position. The name of that game is to be in that game.