MAke sure you dont have enough money on you to catch the bus so therfore you have to walk. You will soon become used to it and not even think of the bus.
I walk (up to 4 hours some days) i know that i am obbsessive. I completeed a marathon 4 weeks ago and i have a duathalon to do in 3 months.
I find enrolling into something gives me a goal. I know i have to keep up fitness to compete in sept IYKWIM.
My ds is 7 and will walk up to 15 miles in a day. He hhas to walk with me and dogs at weekend etc. Ypou will have to get used to other parents telling you you are cruel for making them do it but i dont fore my son to walk he likes it.
If your children are young enough i used to take pasta out with me and every 5 mins of good walking he 'earnt' a bit of pasta, when we got home we added up his pasta pieces and exchanged each piece for 5p, you gradually increase the time between pieces and increase money value.
Also someone once said to me about running ' if you can run for 5 mins you can certainly run for 10 etc' and i have to say this is something i use for all my fitness stuff, it certainly works for walking and gym. apply it and see what happens.
Also another little thing is if you have several items to take upstairs take them seperatly over the course of a day, it is amazing how many times you climb the stairs.
Just dont start of by pushing yourself too much, you have to push yourself to some degree but dont over so it, listen to your body and take it from there.
Most of all enjoy yourself and keep going.
I hope that long winded post helps!