My DD is 7, and luckily, because we live in an outlying village to the one her school is in, the school mini-bus collects her in the morning and a small handful of other similar kids and drops them off each evening.
However, I did do the run for a short while while she was settling into Year R, and I met a some lovely Mums, one of which I see socially out of school and would say is a good friend. I know others, and their names, but because I don't rock up at the school on a regular basis, they ignore me on the few occasions that I do. The downside to this is that DD does not get invited to many parties, which is hugely unfair as her teachers always tell me how popular she is, so it MUST be that Mums decide who gets an invite and who does not. For the most part, this makes me feel bad, but I guess if she doesn't know, it's fine.
DS has started nursery and because my DM or DH usually collect him, I see the same thing happening there too - there are Mums which seem to have evolved into BFFs in the space of a year and I just don't get how that happens - I am friendly and talkative but must manage to look very, very invisible!
So yes, it's not a pleasant thing, but we all probably feel a bit the same so I just remember that.