I don't understand a joke, please explain.

Buffet hotpot, free for each 30 yuan, height 1 children under one meter.

Hot pot city is to attract parents with children to bring their children to a buffet.

Because children under the height 1 meter don't eat much.

Therefore, hot pot city allows children under 1 meter to be free and not lose money.

The aunt in kindergarten only needs 30 yuan (the money for her to eat buffet alone)

Then take 50 children in her class who are under 1 meter to eat a free buffet.

1 height 1 children under the meter can eat free buffet hotpot city.

50 children under the height 1 meter will lose a lot of weight after eating the free buffet hot pot city.

So the joke is that the hot pot city smashed its own feet.