Tell a story about the two children in the photo. What are they doing now? Who are they? What do their lives look like? Who will they become?
Journal about your earliest memory. Think back on an important moment in your growing up and write about it. Describe your childhood bedroom, a classroom, the neighborhood pool.
Visit a character when he or she was a child. How did the events and circumstances of their childhood make them who they are, for good or ill? What does your character remember as significant? (Is their memory reliable?) Watch them interact with surroundings and family members when they are young. You just may gain some valuable insight that will make them well-rounded characters that engage your readers.