There should be a sweeping, devastating novel in the Children's Crusade of 1212 A.D.--the deadly attrition, the psychology of demagoguery, the limits of faith, the complex social and religious background. This isn't it. Rhodes follows the German children's trek (there was a French one as well), but instead of penetrating deeply or reaching panoramically, he goes the Classic Comics route with one goody-goody trio: English Roger, French teen beauty Laurelle, and horny monk Harolde. Along with secretly Jewish and vaguely Zionistic Jonathan, they follow child prophet Nicholas out of apparent doltishness and lip-service religiosity--and take on the dangerous Alpine job of scouting ahead for the 20,000 children marching south from Cologne. To complete the reduction to melodrama, Rhodes has a bad baddie too: half-caste white-slaver Frizio, who pursues the kids down through Italy and whips them off on a slave ship to Alexandria for prostitution and starvation. Though he has obviously done his research, Rhodes is too busy turning his characters into saints and their story into the R-rated Adventures of Sinbad to provide any rich sense of the places through which the children stagger or their reasons for doing so. The dialogue is Hollywood-epicky (""Have you ever wondered at the strange sequence of events which has brought us to this remote edge of the world?""), and the narration at best workmanlike (at worst, ""Guilt beat its raven wings around his head""). Still, some readers will welcome any long scenic swash that buckles--even if it turns a fascinating subject into a Mantovani rendition of ""To Dream the Impossible Dream"" as filmed by C. B. de Mille.