Kid walking down the road as Jimmy drives by. No different than in any other movie where a car whizzzes by a stunned pedestrian. Did we need to know their relationships to the drivers too?A reason for being there.Friend of Jimmys. What more do you really need?As I said, "Who the fuck is that kid and why is he there?"
His existence is random and not all explained or explored. Thus, he has no reason for being there. It's the first rule of storytelling.