It has been topic of controversy, but recent studies show that curds or yogurt given in normal temperature can actually act as immunity boosters. Curd have healthy bacteria that can actually increase immunity. It has been an old concept that it increases mucus productivity which is wrong. Effect of fermented milk on upper respiratory tract infection in adults who lived in the haze area of Northern China: a randomized clinical trial Hong Zhang, Junli Miao, [...], and Zhenmin Liu This has been a study done in 2021 shows yoghurt along with probiotics can mitigate upper respiratory tract infection. But any food for a child should be given in moderation.