Your 20-month-old is probably still doing some functional play, but more and more symbolic (pretend or dramatic play) as well. Play with your toddler when you can to encourage this symbolic play as it fosters creativity and imagination.
Continue to provide your toddler opportunities to play with other children. Try to keep playdates simple and somewhat structured. Large groups may be intimidating for your toddler if she does not have a lot of experience with other children. Children who go to child care are usually more comfortable around larger groups of children, but still require some structure.
Sharing toys still does not come naturally and she will need a lot of help in this area. She does not understand the concept of sharing yet as her toys still sometimes feel like extensions of her. You can practice sharing when other children are not around. Pick up a toy and play with it beside her, then say “your turn” and give it to her. Ask for it back after a few minutes and if she is willing hand it over, praise her for sharing. Play with it for a minute then give it back to her so she understands that “sharing” involves getting the toy back. This is a skill that will still take some time to mature. If you are having other children over to play and sharing is difficult for your child, there is nothing wrong with hiding some of the favorite toys away to avoid tears.
Try to incorporate letters, numbers, colors, and shapes into your toddler’s play. Talk about these concepts while you play with her to start to make her familiar with them.
References:
Pellis, S. M., & Pellis, V. C. (2006). Play and the development of social engagement: A comparative perspective. In P. J. Marshall & N. A. Fox (Eds.), The development of social engagement: Neurobiological perspectives (pp. 247–274). Oxford, UK: Oxford University Press.
Hirsh-Pasek, K., & Golinkoff, R. M. (2016). Becoming brilliant: What science tells us about raising successful children. Washington, DC: American Psychological Association.
Hirsh-Pasek, K., Golinkoff, R., Berk, L., & Singer, D. (2009). A mandate for playful learning in preschool: Presenting the evidence. New York, NY: Oxford University Press.