If the kids don’t mind sharing a room:
http://www.sykescottages.co.uk/cottage/Yorkshire-Dales-South-Grassington/Sandywood-2613.htm%5D
Had a lovely long weekend here with the wife and dog when she was a pup. Not near the coast, and not a huge place, but in one of the best parts of the Dales. Plenty of things to do around and about, large utility room for wet dog and muddy bike storage, great trails from the doorstep and the legendary The New Inn a short walk down the road at Appletreewick. Looks like it’s booked up for most of this year, but definitely one worth considering for the future. Also, little mice carved into the woodwork around the fireplace! Nearly made me cry tears of joy that there are still craftspeople out there.
If the kids demand a room each:
http://www.gallowaycountrycottages.co.uk/folder-14-bridgend-cottage%5D
Big place literally across the road from the beach. Various Stanes within touching distance (Dalbeattie a couple of miles up the road). Large garden and stream (handy for dog cleaning) out the back and a secure shed, built under part of the house, for bike storage. Rockcliffe and Kippford just up the road. We took our daughter here when she was six months old and had as damn near a perfect time as you could wish for. Really happy memories of our stay there, we’ll definitely return.