So far as I know there is no book on the fundamentals of architecture for fourth and fifth graders, nor has there been one since The Young Architects by the Stanley-Browns. Here, in story form, a considerable amount of information is painlessly conveyed. Bored at school and despondent about spending the spring holidays with an unknown uncle and aunt in mid-England, 12-year-old Jennifer hears a lecture on old buildings that sparks her interest. Then on the train she meets Jim, 13, finds that he wants to be an architect -- and that he, too, is bound for Grantley. With the help of Jennifer's aunt and uncle, the youngsters start notebooks and drawings, and as they learn more and more about the old town buildings, churches, manor houses, the details of their construction and the histories connected with them, the holidays prove rewarding. This goes more seriously into its theme than comparable American books, and should appeal if the right readers can be found.