If you've arrived by Search: this site is devoted to "family holidays" and you can find ideas by clicking just about anywhere. If you're traveling from the UK to the US or Canada, below are some good starting points.
Florida is definitely on the map for UK visitors, thanks to family holiday and theme park mecca, Orlando, with Disney World, Universal Orlando, and more. Stay two weeks, and combine a week at the theme parks in (inland) Orlando with a getaway at the beaches a few hours away.
Kids of all ages will find fun in the Big Apple. To name a few highlights: harbour tour on "The Beast"; Blue Man Group; movie tours; Top of the Rock; great museums; amazing toy stores. Bonus: volunteer "Big Apple Greeters" are ready to show you around their town.
Hershey is a favorite family holiday destination in Pennsylvania. Kids love the Hersheypark theme park, built by chocolate tycoon Milton Hershey. Visit during summer, or in October for Hershey Park in the Dark, or during "Christmas Candylane". Stay at the classic Hotel Hershey (with kids club, and chocolate-themed spa) or at Hershey Lodge.
History comes to life in Colonial Williamsburg, as actors and volunteers portray people from the 1770's just before the American Revolution. And nearby is some just-plain-fun, at Busch Gardens Europe theme park (rides, shows, etc.) and Water Country USA giant waterpark.
Dude ranch family holidays can offer the wide open spaces and perhaps the lingering mystique of the Wild West. They're an easy type of family holiday, too: meals are included, and fun -- in the form of horse-riding-- is right on-site. (Not always included in the pricing, though.) You can be a dude in Arizona, Colorado, Wyoming -- even New York State.
Resorts with their own water park pile on the fun for both winter and summer family holidays. The Great Wolf Lodge brand, for instance, offers large suites, Grand Lobby with giant fireplace and storytelling, "dry" play zones, "Howl-o-Ween" and "Snowland" seasons, not to mention giant indoor water parks, and outdoor water parks in summer at some resorts. (Aveda Concept Spa, too.)