OK i guess that changes things. Boston has lovely weather in May. There is a lot to do here. Museums (my personal fav being the Children's Museum), six flags in NH, Canobie Lake Park, The Freedom Trail (which includes Faneuil Hall and the U.S.S. Constitution), a ride in the Duck Boats, a cruise in the Boston harbor or a picnic by the Charles.
now you are talking... :P.
how can you forget the exotic and most delicious desi food from Madina Market :)...btw, six flags is in Mass, but kind of far and its near CT, however Canobie is NH, just on the egde of MA and NH Canobie lake park is like 30 minutes drive from Boston.
Canobie lake is my favorite. and there is another one with the name Water Wizz in Cape cod.. these are all excellent family these parks.
Children musuem is excellent, along with Boston Duck tour which also takes a splash in the charles naddi (river).