Waterville is nice for brining the family. I would never think of going there for real DH, but they do a great kid/non-rider friendly cruiser off the lift (Livermore road) and if you stay in the valley (we like the Black Bear Lodge) the lodging comes with a bunch of free passes for a couple hour bike rental, a chairlift ride, paddle boats etc. Bunch of nice easy XCish stuff around the resort area, maps at the bike shop, everything is walking distance, very scenic. You can put together some serious backcountry-style XC rides in the area on some of the hiking trails and dirt roads out there, just be prepared to be in the middle of nowhere by yourself, riding hard. (Sing out if you want some more details).
Definitely check out Jiminy Peak also. TONs of stuff at the base to do (alpine slide, mountain coaster, etc) and they run the lower lift til dark, so it's easy to do some family time plus get some riding in. Not up on the details for XC, tho I know they did the Pedrosfest in the area for years, but if you're looking DHing, Jiminy is leaps and bounds (and more leaps) beyond Waterville. Bit pricier, specially for the activities, but it's also nice.
Slapheadmofo Leisure Team
Sunday River Bike Park