As the coach of my son's team of 13 year olds I can say with much conviction that as I much as I enjoy being on the field with my son and a few of his teammates I can not wait for the next three months to end.
I see a lot of what the OP is saying. Practice has become optional for some kids and their parents. I am not talking about the 10th or 11th kid on the roster. They always show up and work hard. I am talking about one of our top two pitchers and one of our top two hitters. It is like the attitude is that they are good enough so they make some excuse not to make the effort to come to practice.
This is not some rec team either. We are very competitive in a very competitve part of the country. Maybe it is simply the natural process where even talented kids start losing interest in one sport or the other.
I know you say myself and the other coach should simply sit them, etc but on a team where you have Dads as volunteer coaches and everyone knows everyone outside of baseball it simply is not that easy. Best to bite your tongue and accept it for what it is.