Canny folks, the Epsteins (as if we hadn't known before). Here's Charles Wilson Peale, who ""took for granted that his children. . . would be interested in everything that interested him,"" inviting young Rembrandt and Raphael and Angelica (""each named after a famous painter"") to watch him unpack and draw--bones, big bones. ""Trying something new"" is his greatest pleasure; besides, his drawings are going to be paid for, and celebrated painter that he is, ""he was still regularly out of blast, as he put it."" Another few pages, and you've learned that the new natural scientists, having rejected divine creation, ""were coming close to discovering the idea of a constantly changing world"" 75 years before Darwin's formulation of the theory of evolution. You know, too, that Mr. Peale is hoping that an American mammoth will turn up with bones at least as large as those of the recently disinterred Siberian mammoth: ""He had been annoyed when a French scientist, the' Count Buffon, declared that all animals in America were smaller than the animals of other continents."" There follows, in time, the difficult, dogged search for the bones of the Great American Natural Wonder, and its reconstruction--spirited along by the reader's appreciation of its import and the host of motifs (literary, anecdotal, factual) introduced at the outset. The drawings are heavily indebted to Robert Lawson--but for crisp delineation, there's no better model. The stylish fancy of Margaret Cooper's Great Bone Hunt (1967) is not to be dismissed; this, however, will capture the imagination of children with a more down-to-earth bent. It instructs as it delights.