Multiple generations can easily spend a pleasant week or so sharing seaside adventures. You’ll start off in coastal Maine, then work your way south to visit the somewhat warmer waters off Massachusetts and Rhode Island. If you don’t have time for this full itinerary, break it in half, doing the Maine-Cape Ann half on one trip and the Cape Cod-to-Mystic trip another time.
Days 1 & 2: Portland
Portland, Maine, your base for the first 4 days, is a joy for families. The Children’s Museum and Theatre of Maine is almost exactly in the center of the city, making it a good jumping-off point for a walking tour. The excellent Portland Museum of Art, right next door, provides teens with something different to do.
In the historic Old Port, Exchange Street is the key shopping address. Kids will enjoy the ice-cream shops, boats, and quirky gift stores.  
The Maine Narrow Gauge Railroad Co. & Museum combines a short train ride to the foot of the cliffs framing Portland’s east end with a museum.
If the kids need to stretch their legs, the mile-long paved Eastern Prom Pathway offers sweeping views of the harbor and offshore islands. (At its eastern end, you can hop on a Casco Bay Lines ferry to sail out to some of those islands.) Stretching inland, rambling Eastern Promenade park is ideal for a picnic or a casual ball game.
For baseball fans, an outing to Hadlock Field to watch the Portland Sea Dogs can’t be beat; it’s one of New Englanders’ favorite minor-league parks.
Finally, young and old alike enjoy the sunsets, picnics, sailboat views, and swing sets of the park along the Eastern Promenade.
Day 3: Cape Elizabeth
Plan to spend at least one afternoon hitting the string of beaches and lighthouses off Route 77 in the quiet town of Cape Elizabeth and surrounds, just 15 minutes from Portland.
Don’t miss Portland Head Light and neighboring Fort Williams Park with its fortress ruins and children’s garden. Then, romp around in the sand and surf at Crescent, Scarborough, or Willard Beach.
Day 4: Old Orchard Beach
Drive 30 minutes south of Portland, and you come to Old Orchard Beach. This place may strike you as corny at first, but it rarely fails to entertain with its amusement park and miles of sandy beach. On the photogenic pier out over the water, you can find restaurants, bars, bad-for-you eats (mmm . . . fried dough), and souvenirs.
Day 5: Cape Ann
Leave early for your long drive south. Detour east in Massachusetts to stop off in downtown Rockport for souvenirs and fudge, then push on to Halibut Point State Park, at the tip of Cape Ann, which boasts spectacular views and plenty of room to run around. On your way back to the highway, take Route 133 so you can lunch on fried clams at the legendary Woodman’s of Essex. Skirting Boston, continue on to Cape Cod, where you’ll be staying for the next 3 nights. Base yourself in either Brewster or Dennis. Either way, grab a quick and easy seafood dinner at Captain Frosty’s in Dennis. 
Days 6, 7 & 8: Cape Cod
On your Day 6, hang out at the child-friendly beaches that front Cape Cod Bay. On Day 7, get up early enough to be at the Heritage Museums and Gardens in Sandwich by 9am, and don’t expect to get away without a carousel ride. Book in advance if you want to try the rope course at the adjacent Adventure Park. Then, in the afternoon, head south to Falmouth to visit the Woods Hole Aquarium. Cap off the day with some mini-golf or, if it’s July or August, an evening watching game in the Cape Cod Baseball League. Finish off your Cape Cod adventure on Day 8 by visiting the Cape Cod Museum of Natural History in Brewster and taking a bike ride on the Cape Cod Rail Trail
Days 9 & 10: South County & Mystic
Work your way west from Cape Cod along the Rhode Island coast, making sure to stop off in Westerly for a little beach time or a ride on the vintage carousel. You’ll reach Connecticut in time to explore the Mystic Aquarium. Stay overnight in the Mystic area and be up bright and early the next morning to spend a full day at the living history park Mystic Seaport Museum.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.