Masks conceal facial nuances which are very important to young children developing ability to recognize social cues. The article makes it sound like this is only a problem for people with language difficulties but it is obviously much broader than that: https://www.wsj.com/articles/covid-face-masks-are-disrupting...

The article also touches on distancing as one of the key measures helping reduce flu and colds, and this is probably the one most responsible for the huge surge in children's psychiatric visits and suicide attempts over the past year, which somehow didn't rate a mention in NPR's discussion of the cons.