他们在课间休息英语可以说成 "They are on a break between classes."
"break"在这里表示"休息"，"between classes"表示"课间"。
例句：
They are on a break between classes. (他们在课间休息)
He takes a break between classes to grab a snack. (他在课间休息时去吃点东西)
She uses her break between classes to catch up on homework. (她在课间休息时用来赶作业)