A couple of articles from the National Association for the Education of Young Children emphasize the importance of play in learning, from the notion of “guided play” to pointers on the kinds of play conducive to learning in toddlers.
The Case of Brain Science and Guided Play: A Developing Story by Brenna Hassinger-Das, Kathy Hirsh-Pasek, Roberta Michnick Golinkoff
How to Support Children’s Approaches to Learning? Play with Them! by Gaye Gronlund