I just read a fascinating article by Lisa Scott, Associate Professor of Psychology and Director of the Brain, Cognition and Development Research Lab at the University of Florida, that reinforces earlier research which says that babies love looking at faces, will look at a face longer than anything else, and thus faces are important educational tools for babies.

https://bold.expert/the-importance-of-faces-for-infants-learning/

Smiling at people puts them at ease and creates connection.  Image how much more powerful it is, then, to smile at your baby!