Honestly, it's probably just because you are a parent and they are trying to impress each other. Who can be the most bold and get away with it. If you can figure out what grade they are in, just go speak to a year level teacher and say you've seen some students displaying disrespectful behaviour after school towards parents and perhaps they need to be reminded that in school uniform leaving school they still need to conduct themselves in a responsible manner. It might be enough to deter them. If its really causing you distress I agree with a PP, change where you do pick up and avoid them and their path completely.