Shadows, and how they change according to the movement of the sun, are complicated and fascinating topics.
Have some fun with them. Go out in the morning on a sunny day with your child and observe your shadows as you walk, run, dance, and chase one another. Then get some sidewalk chalk and invite your child to stand in an agreed upon spot (mark the spot with an X!) while you trace her shadow.
Go out again several times throughout the day. Have her stand in the same spot and trace her shadow each time.
How did her shadow change? When was it the biggest or the smallest?
For an extension activity, give chalk to your child and invite her to trace the shadows of stationary objects then, check them throughout the course of a day.