Life in Celtic Times Coloring Book
If your children like to color, why not capitalize on their interest by supplying them with a study of an ancient civilization at the same time? While nowhere near a complete study, the accompanying text is interesting and informative. As with the Field Guide Coloring Books, coloring these scenes while studying is probably a good way to fix a picture in the mind's eye and help you to retain images of that civilization.
Personally, I favor the idea of actually "being there" via period costumes, customs, festivals, and other props to re-enact life in these periods. However, I don't have the time (or remaining energy) to do all this. But I can sit down and color with my kids while we talk about the past. No preparation, no planning, no time demands. It may not be "the best" way to relive the past, but it's an enjoyable alternative that fits with my time (and energy) limitations!