A megacity in south China has become the first in the country to pass a law promoting breastfeeding, which remains unpopular despite the myriad proven benefits of human milk.

The law, passed in Guangzhou, requires public places such as train stations, museums and parks to set up dedicated lactation rooms, or face fines. Employers must provide breastfeeding mothers with a one-hour daily break to feed or pump.

It also bans hospitals and medical institutions from taking money from or…