Take the train from Boston North Station to Rockport

http://www.mbta.com/schedules_and_ma...route=NBRYROCK

Its a short hike (0.6mile)from the station to the Motif and Bearskin Neck. Yes there are some cabs around...

http://www.cape-ann.com/bearskin.html

your wife and kids will have plenty to do at this location. Lots of small shops, and some interesting places for lunch. If you kids have never experienced a train ride, they'll have fun watching the urban scenery go by until you get well out of town...