An oversize book (10''x13'') with attractive cut-out color photos of children and objects, their delicately sketched backgrounds on generous white space, preserving an uncluttered look. A great many concepts are introduced here: days, weeks, seasons, years; different kinds of clocks, including digital, analog, and even a sand clock, and their history; words and symbols used for time's passage. There are lots of clock faces, exercises (mix and match pages: find the clock showing ``twenty- five after six''), a glossary, and a large fold-out clock with sturdy moveable hands. The clear, detailed text is peppered with rhetorical questions, but the didactic tone is not inappropriate to the subject. A thorough and useful presentation that includes a sensible note addressed to adults. (Nonfiction. 4-8)