Not a cottage, but our lovely holiday house is still available over Christmas and for a short break between Christmas and New Year. The house is very well equipped for young children but my own teenagers enjoy staying there as well as there is a Spa with indoor and outdoor pool, a gym, sauna, steam room. Plenty of pubs in the surrounding area for meals out and lots of walking and cycling.
The house sleeps 8 so maybe too big for 4 of you but maybe you could have friends or family join you.
www.falcon-house.com