I think you have your pick of time periods- Roman, Viking, Norman, Medieval, Renaissance, Modern. I would see what regions you will visit and what sites you are interested in and go from there. Some sites have tremendous historical overlap. The York cathedral or York Minster had Roman, Norman, Medieval and many other periods represented in a single structure. The power for us was to see how each new group built on the past. I think it is helpful to look at the web sites of the really big sites you plan to visit. The National Railroad Museum in York for instance has various talks and opening of historic cars at specific times of day so I planned our trip to include getting a chance to step into "The Mallard" as that was important to us. We paid for audio tours of historic places-usually the adult audio tours. My son was 6 at the time and would listen to the whole tour. This gave us a lot of history and the ability to start and stop as needed. I should add that he is probably an auditory learner.