It really depends on how many is in your group, and how far you think "walking distance" is. I was really out of shape when I started daycare, and 4.5 km one way seemed really far to me. Now I walk it both ways regularly, and bought a stroller that could accommodate all the little legs (a runabout). It really has opened up a world of possibilities to us (library, fire station, spray park, playgroups, etc.) and has stopped me going bonkers being cooped up in the house! Great exercise too!!

For the bus, I find my limit with the age group you listed would be 4 but I prefer 3. Anymore I have found is tough to manage. I wear the youngest in an ergo, put two in a double stroller and my oldest (almost three) would walk and sit on the bus with me. Anymore would be hard on me with the next oldest being 14 months, so good luck to you!!