We are from NH and Maine and I can tell you we have devoted 1 week each summer plus many many weekends and overnights---- 1 week is not enough for the entire 'tri-state' region:
Old Orchard Beach: big hit with kids-- amusement rides at the board walk-- fireworks every Thursday night are a big hit. Trolley runs to many of the campgrounds- won't need a car. Powder Horn is where we usually stay--.5 mile from the beach; Old Orchard is a 1.5 hr drive for us and we do a Thur - Sun weekend every year.
Bar Harbor- aka Acadia National Park--- A MUST-- KOA Oceanside is where we have stayed- they are on the Shuttle bus route- so you won't need your car- which goes thru out the national park.
Drive Rt 1 up the coast to Bar Harbor-- Camden State Park woul be perfect stop over.
Depending upon your route-- after Bar Harbor head west to Rt 2 into White Mountains then down Rt 16 thru Pinkam Notch into North Conway-- we have camped at Green Meadow in Glenn--- quiet/family campground.
Rt 302 heads west out of N. Conway/ Glenn to Montpelier Vermont; or back up to Rt 2 and head west to Montpelier where you can see the Green Mountains and Burlington-- I have stayed at a very nice state park right on Lake Champlain just north of Burlington.
Have a great trip--- We love Northern New England in the summer!!