The key features of the painting are:
Muted colors: Cassatt used a subtle color palette. Muted greens, purples, blues, and oranges. This gives the painting a soft appearance.
Leading lines: We want to look where the mother and child are looking.
Color in the shadows: Cassatt, and the Impressionists in general, used color in the shadows rather than blacks and browns.
Simplification: Cassatt didn’t paint every detail. She simplified the scene into basic shapes and colors. The rest is up to our imaginations.