According to a study published in JAMA Pediatrics, a large proportion of healthy preschool kids could recognize the emotions shown in static pictures of adults with and without face masks.

In the cross-sectional study involving 276 preschool children, investigators assessed the effect of masks on their ability to identify joy, anger, and sadness. The kids saw pictures of 15 actors with and without surgical face masks. Around 68.8% of the children could correctly recognize the emotion portrayed in the photograph. The correct response rate was 70.6% for unmasked faces and 66.9% for faces with masks. Correct identification of joy was found to be significantly higher for unmasked faces compared to faces with masks (94.8% vs. 87.3%). Similar was the case for correct identification of the emotion of sadness (54.1% vs. 48.9%; P < .001 for both). However, there was no significant difference in recognition of anger for unmasked and masked faces (62.2% vs. 64.6%, P = .10)… (Medscape)