in the US can vary from state to state or region to region. I'm in Eastern Pa, and our calendar goes August to July. Depending on the level of team you are coaching, you can have June and July "off". Some of the biggest tournaments are played in May, and for most teams, that's where it ends. Regionals and Nationals are played in June and July, so some teams keep busy over the summer months. But there are far more players off during the summer months than not. Is that a problem?
There are more variables here than I can cover. Vacations, summer teams, over-seas trips, soccer camps, family in different parts of the country, private training or just actual rest. You get the point. As a coach, how do we support our players? I like setting my schedule early on, and that seems to keep everyone happy. I understand the need for downtime and family fun. I try to be understanding and by setting the expectations early on, at least everyone can get on the same page.
Balance is key here. Allow them to do a camp, go on vacation, train on their own. Sans the guilt. We as coaches have the obligation of preparing our players for summer/fall tournaments. A part of that may be creating off-season workout plans, giving them training resources or even running sessions with 3/4 players at a time. As coaches in the US, one of the things we will never get credit for is adapting and being innovative with the way we coach our players. The best thing we can do is support our players, encourage them to take time off and teach them about off-season discipline. If you have a good trainer you can recommend, send them there. If you know about good camps, let them know. Plan in the winter. Keep parents involved and informed. Balance for them and you, will do wonders for you next season.