Meaning:

“神兽” means “magic beasts,” “归” means “to return,” and “笼” means “cage.” Literally meaning “returning the magic beasts to their cages,” this is a joking way of saying “sending kids back to school.” Calling their children “magic beasts” reveals the mixed feelings of parents toward their young: The kids are precious but hard to manage. As a new school semester begins, many parents feel relieved after sending their kids back to school, hence the saying “returning the magic beasts to their cages.”

Example:

A: 你今天怎么这么早来健身？

Nǐ jīntiān zěnme zhème zǎo lái jiànshēn？

Why are you so early to hit the gym today?

B: 今天开始神兽归笼，我的假期开始了！

Jīntiān kāishǐ shénshòu guīlóng，wǒ de jiǎqī kāishǐ le！

The new semester begins and my kid is back in school. So it’s my turn to enjoy a vacation!