Hi Tonette,
Welcome to
RP!
This is the best I could do for this picture

... As to why that happened beside the fact that it was taken 'against the glare of the sunlight' ... or what to do to prevent it happening again when taking pictures, I really can't help ... (I'm no good in taking pictures ...

).
Working with Photoshop, once lifted the shadows, as Janet said already, there were practically no detail to work on on the faces of some of the boys/girls ....
What I did to bring them out a bit is:
- Selected the most faded faces.
- Created a Levels adjustment Layer for the selection and increased the contrast a bit.
- Created several new Empty Layers, blendings: Overlay, Screen, Soft Light, Color, Lighten, Darken to emphasize, correct and improve.
Hope this helps ... a bit ...