The crying baby is irrelevant, apart from the emotive "ah, bless" element. What is of importance is the screaming and uncooperative behavior of the adult(s) when asked to pull over. Yes, they might have not been involved in any unlawful activity; however, that's all in retrospect. Are you suggesting, Gromit, that the police cannot act upon the belief that they suspect a crime has been committed or is about to be committed?