here are some great tidbits froma  list sent out by another twins’ mom:

Museums:
Children’s Museum – on Fridays, open until 9 pm, admission is $1 after 5 – www.bostonkids.org
Aquarium – www.neaq.org
Science Museum (has a discovery room – great for young children) – www.mos.org
Museum of Natural History at Harvard (animal exhibit, etc.) – www.hmnh.harvard.edu

Pools that offer day passes:
Sonesta Hotel across from Cambridgeside Galleria
Seaport Hotel in South Boston
Marriot Longwharf
Marriot Charlestown
Charlestown YMCA
Indoor water park in Danvers – http://www.cocokeywaterresort.com/locations/danvers/index.aspx

Theatres:
Puppet Showplace in Brookline – http://www.puppetshowplace.org/
Regent Theatre in Arlington – www.regenttheatre.com/

Farms with Animals:
Drumlin Farm in Lincoln – www.lincoln-ma.com/town_groups/drumlin.htm
Codman Farm in Lincoln – www.lincoln-ma.com/town_groups/codmanfarm.htm