every parent break down in tears when they saw their children coming backbreak down

break down 失声痛哭
= lose control of one's emotions

· He broke down when he heard that his bird was dead.
当他听说他的鸟死了，就哭了起来。

To have a physical or mental collapse.
使健康、精神崩溃

崩溃

大概就是"倒塌,崩溃"的意思吧
break down in tears 就是"禁不住流泪"

每个父母当看到他们的孩子们回来的时候,他们都忍不住痛哭流涕.
break down in tears "禁不住流泪"这个都是习惯搭配了啊.
break down是指"垮掉；崩溃".

break down：垮掉；崩溃
break down in tears: 痛哭流涕；泪如雨下