Dagenham you see there are two examples you've mentioned of rudeness already with you!
Went on nice walk today, on path in park, 2 women at a guess in 30s, narrow path, had to step on grass to get round (never mind didn't bother me), luckily on way to park saw a few people in street with and without prams, pregnant or not pregnant seemed fine. Noticed a set of 6 people with kids and buggies but walked 2 abreast but on a fairly wide pavement but behind the other, fine again.
In park no bother generally most people fine and well behaved, day. I did notice on the way back though coming up a hill and round a corner where there was a lively young girl at a guess 3 or so? Her grandmother (it looked like) said to her "be careful of the woman" meaning me, other adults with her were oblivious - I didn't care either way just smiled and walked past.
It does make you wonder though for every mum with a buggy hogging the pavement their parenting must cascade down to their children, eg letting people pass etc.
I've been brought up to always hold doors open, help people, be polite, use manners etc and I'd do that if I were a mother or not. The vast majority of people I come across "are" polite and helpful, but there are quite a few who aren't...