Pupils at Suan Lumphini School assemble each morning under a colored flag indicating the day's air quality—red for worst, yellow for second worst, blue for best.

Thailand registers dire air pollution levels annually—its cities topping the world's most polluted for days last year—and children face the greatest risk of long-term damage to their respiratory systems.

Lalipthat Prakham, who works as a maid, said it has already made her eight-year-old daughter sick.

"I always try to make her wear a mask. I tell her to keep the mask on at all times and to avoid going outside," she told AFPwhile waiting for her child outside Suan Lumphini.

Prime Minister Srettha Thavisin has promised to tackle the issue, with his cabinet in January approving a bill aimed at tackling dangerous levels of PM2.5—particles so tiny they can enter the bloodstream.

But in the meantime, residents must endure.

Nanthnan Hajiub said his 11-year-old son has developed a sporadic cough.

"I'm worried about the pollution, and the effect it is having on his respiratory system," the 45-year-old business owner said.