My family and I went for a hike at Cornell Farm in South Dartmouth over the weekend.  The kids absolutely loved it.  The walking trails were quite accessible for just about everyone.  In fact, we saw a number of people hiking with strollers.  There were several bridges including one suspension bridge that was wobbly enough to get the adrenaline pumped (even though it was perfectly safe).  There was plenty of parking, and the entire experience was free.  Such a good time! GREAT, quality family time.