During a previous assignment, I was told that during the summer period I was going to be swamped with work, and I was asked, because I don’t have kids, not to take a vacation in that period.
So I didn’t and told them that I would take my vacation after the summer holiday period, in October. I told them this in May.

The summer period comes around, and it was the slowest period I had ever encountered. There was literally nothing for me to do. Meanwhile the project manager and a number of other people in my team, who had small kids, did take time off in the summer period. By the time it was October, the work had picked up again, and they complained that I was going to be on vacation in that period. The manager called me not a team player. I just told them that I held the fort when they told me to, and that I had communicated this vacation well ahead of time. They had had their relax time, now it was time for me.

I agree, I don’t want to make things harder for my team members, but within reason. And what they asked of me wasn’t reasonable.