The coast north of Boston (and into New Hampshire) is quiet and nice and not quiet as pricey as the Cape.

My family goes camping in the summer on the Connecticut shore (Rocky Neck or Hammonasset State Parks). There's not much to do but sit on the beach, go crabbing in the marshlands, or fish, but the beaches are great for kids.

If Jersey isn't too far for you, the Jersey Shore isn't nearly as bad as Snookie & Company portray it to be.

Cape Cod offers a number of options near the beach with plenty to do for the whole family. The following web page gives you a list of some favorable recommendations: http://bit.ly/bhTQ5u

Another option would be Narragansett where some vacation rentals are listed here: http://bit.ly/c8X3MX