All out other UK trips have been May half term, but we have done the following (all driving so we had the car for days out).
Chester - walked the walls (downloaded an interactive app) and city, Chester Zoo, Anderton Boat Lift (I grew up locally and we picked up my Uncle who has Downs and took him), Beeston Castle (childhood thing - don't bother!), then Styal Mill on the way home.
Stratford (actually stayed in Redditch) - Shakespeare's house, Anne Hathaway's farm, butterfly place, walled around Stratford, other things I can't remember.
Canterbury - walked around the city, couple of museums, castles - Dover, Deal, another one I can't remember and one on the way down, animal place then Chatham Maritime on the way home.
I booked apartments for all of the above, but if I was just going with my boys now I'd look for cheap travelodge or premier inn rooms and share.
We also did a Hoseasons lodge in April this year at Cheddar Gorge and that was really good.