I funk too many preschool teachers overthink and doubt themselves.
If you drew a circle, and a stick line below - the kids would say you drew a tree. These are 3-5 year olds. They are not Picasso.
Art for kids is letting kids explore the art medium. I only have three primary colors of paint in my class. The kids learn how to mix colors for their projects. They scribble away in shaving cream on the table. Play dough, clay, wax sticks. There are so many ways kids can express themselves. I have a studio corner, and follow the art masters through the year. October is cubism. I have books and posters about the art style in the classroom. The kids can do block prints. Or can cut shapes to make a collage. Realism month is drawing still life (a bowl of plastic fruit or whatever they want), and portraits of each other.
Preschoolers are wonderful and curious explorers. Join the journey with them!