If you can one kid - there is no problem really. Walk him or her to school in the morning, ask grandmother to bring them back etc.
When you have more than one - it is entrily possible they will end up going to different schools and after the school one of them had to go to the music shool and the other one to his hockey team or something etc etc. You simply can't do this without a car.
I was the only child in the family so we never needed a car for this kind of scenario, plus we were living in a relatevely small city (450k), so public transport was more than enough for me, but this is not always the case.
>and then walk a couple more blocks to work.
yeah, now imaging you have two of them going to two different schools, each 40 minutes walking distance from home, different directions and your office in somewhere else too.