M.P.
My children took lessons when they were 4 and 6 years old, at the Dedham Health and Athletic Cetner. You do NOT need to be a member to take lessons there. The classes were small, and we were allowed to stay and watch. It was a very positive experience, and my children are better swimmers becuase of it. http://www.dedhamhealth.com/club/scripts/library/view_doc...
They were also enrolled for a few years in the Town of Dedham summer program called "Swim and Gym". It is a combo of gym, swimming and arts and crafts , and my kids LOVED it. Extremely affordable. You sign up for that at the town offices. We stopped doing it only becuase they "outgrew" it.
http://www.dedham-ma.gov/index.cfm?cdid=14812&pid=12026