The acquarium in Woods Hole is a must - walk around and see the "tourists" come and go from the ferry, get an ice cream cone and watch the bridge go up and down at Eel Pond. THere is also a "nature boat ride" - kids pull a lobster trap, take water temp, turbidity, touch tank of local things - but your kids might be a little young.
Go to a Falmouth Commodores - elite college baseball players - many of whom end up in MLB (the Sox recent number One - Morreno played for Cotuit last summer) - but again your kids are young.
Old Silver beach is nice for young kids - on the Bay side and long shallow beach - the South facing beaches drop off quick and can be a little hairy.
Take a day trip on the Island Queen to Martha's Vineyard for lunch and a ride on the merry-go-round in Vineyard Haven
That should pretty much fill up the week
