Adele & Simon By Barbara McClintock Frances Foster Books: 40 pp., color illustrations, for ages 4 to 8, $16 What if you were a conscientious little girl like Adele, with an air-headed little brother like Simon? You'd have a full day. The two live in early-20th century Paris, in a world of soft watercolors based on period illustrations. If it takes a long time to turn the pages, it's because each is filled with detail, from the cauliflower on the cart to the fossils in the natural history museum, to the filigrees of the Metro station entrance. The story is simple: As Simon and Adele travel from the Luxembourg Gardens to the Louvre to a cafe, Simon keeps losing things. His gloves, his crayons, his scarf and sweater all come up missing. Although he's maddeningly untroubled by this, Big Sister is vexed. But just when it looks as though he's going to be in trouble with Mama, all the people they've met that day show up at their front door, carrying all the stuff he lost. Simon is a lucky kid -- and so are the ones whose parents share this lovely book with them.