Why are you assuming that if a cop is talking to a 15-17 year old child that the child is in a gang or has committed a crime? The police talk to lots of people

Why are you assuming that if a cop is talking to a 15-17 year old child that the child is in a gang or has committed a crime? The police talk to lots of people for lots of different reasons and they may interrogate subjects who have not committed any crimes at all for the purpose of gathering information.