Gratitude can be socialized in a similar way... actually having conversations about things that you're grateful for and why you're grateful for these things.

Ashley Ruba

Even with masks being worn, little kids can probably still make reasonable inferences about other people's emotions, i like to point out that the face isn't the most important way we communicate our emotions, it is only one way. We also use tone of voice, we have body posture, we have other kinds of contextual clues that kids and adults can use to figure out how people are feeling.

The risks of contracting Covid from not wearing a mask are probably going to outweigh any slight issue about communication that kids might have.