Bernstein asked California children ""How do people get babies"" and found in their garbled, often amusing answers distinct levels of understanding which correspond to Piagetian stages. Her much-needed book traces these six developmental stages, quoting from the children, generalizing responsibly, and offering appropriate explanations for parents to give--different ones through the years. The youngest children, egocentric and literal-minded, think babies come from stores or hospitals, and distort almost any information; words like ""seed"" or ""egg"" invariably conjure up gardens (the agricultural fallacy) and chickens, so ""sperm"" and ""ovum' are recommended as unambiguous. Belief in magical transformations (""go to the store and buy a duck"") and animist thinking (""does it hurt when the sperm hits the egg?"") persist for several years; the father's part is especially obscure until age seven or eight, and ten-year-olds still have difficulty putting the whole process together. (Once they do, the wonder which young children feel substantially diminishes.) In other words, a one-time explanation won't suffice. Children need successive clarifications as they mature, and parents able to talk comfortably, have a decided advantage: a seven-year-old, given two books by a self-conscious mother, thought that ""to get a baby you must read a book."" Bernstein, a clinical psychologist, also raises those less researched sex education issues that tend to polarize PTA discussions (homosexuality, home nudity) and looks briefly at adult attitudes toward children's sexual play and masturbation, contending ""There is no one right way to respond that rules out the alternatives."" Using a minimum of formal terminology yet never wandering too far from the Piagetian structural framework, Bernstein finds some instructive surprises in the stork's bundle, and her book is a natural selection for adults fumbling in the dark for the right words.