We're from a completely different part of the country and unlikely to find ourselves back in the area again, so wouldn't mind covering a bit of distance to see special attractions
You may want to rethink that 
West Yorkshire alone is a large county and there's so much to do, then you have North, East and South Yorkshire to consider. You could spend a fortnight in either of West or North Yorkshire and you wouldn't even scratch the surface of attractions for outdoorsy families that don't mind the occasional museum/historical stuff.
I'm about half an hour east of Oxenhope but near the 'special attractions worth travelling to' of the Yorkshire Sculpture Park and the Royal Armouries, National Media Museum.
There's also loads of smaller places like Sandal Castle, Pugneys lake, Cannon Hall Farm and Newmillerdam, Roundhay Park, Kirkstall Abbey and Abbey House museum, Thackray Medical Museum, Industrial museums in Leeds and Bradford (eye opening for the average 8 and 11 YO that if they'd been born in Yorkshire in the late 19th century they'd have been working full time in the mills, running under looms and dodging machinery) Temple Newsam and Lotherton Hall all on the outskirts of Leeds - so there you have a week's worth of stuff to do. Then there's York and the east coast.
Closer to Haworth and Oxenhope is Heptonstall, a historical village up the hill with views, easily walkable from Hebden Bridge if you're fit.