It's not necessarily that the child was trafficked as a child. It could be that the child went missing/ran away, lived on the street or in some other bad situation for a while, and then at some point was trafficked. Or it could even be that the child was sent to a relative in another country to grow up there, the relative never took any pictures of them, they grew up there, and then were conned into some trafficking situation as an adult.

Either way, the goal would still be to identify an adult victim of trafficking by the last available picture of them, which was of them as a child.