I don't know, I have an 8 year old dcg that walks alone to the bus stop every morning by herself. I also have a 5 year old that will be starting next month and the only way I would take her is if the mom agreed to let her walk alone with the other girl. It is too hard to get all those kids out to the bus stop twice a day, especially with the cold and snow. I think once the kids get used to the routine of what to do, an 8 year old is old enough to handle it. If the mom gives permission for them to wait for you, then I would see it as a relief that I didn't have to worry about killing myself getting to the bus stop on time.
I am trying to imagine you dragging along a 2 year old with a 1 year old strapped on your back and being pregnant all at the same time - I think you need to do what is easiest for your body, you don't want to over do it. Are you going to be able to handle that when you are 7, 8, 9 months pregnant?