I’m not sure what the appropriate term for this is but I call it “spotty shade”. You know that shade from trees and the leaves from the trees that creates random inconsistent shade? Some people have sunny spots a portion of their face. And they also have shady spots on their faces.

Forgive these not super lovely pictures. But they serve the purpose of a visual example. :)
This picture below has spotty shade from the trees/leaves above them. Do you see the spots of shade and sun on a couple of the kids faces?

Then this picture below is in full shade. Though it’s not the most fabulous or interesting picture. The kids are all in full shade. See the difference?

The simple act of avoiding spotty shade will make your images much better.