Join your local MOMS Club group - www.momsclub.org - you can find your contact through that web site. Dues are minimal, between $25-$28/year (cheap) and the "board" of that local chapter arranges all types of monthly activities, park days, walks, etc. You can always start up your own walking group if there isn't one in your local club, but you'll instantly make many mom friends with young kids right in your area. I've been in mine for 5 years now (3 yr old girl and almost 5 yr old boy). I believe in it so much that I've been the President if my chapter for the past 2 years and Membership Director before that, Activity Day coordinator before that.
There's also "Stroller Strides." You can look them up on the internet if you really just want walking, but I think that may even cost more than just joining a great group of MOMS Club and creating your own walking group if needed.
Good luck!