(FORTUNE Magazine) – It's school time again, and if you'd like to buy your kids something to read -- get in line. Kiddie lit is on the rise, thanks to baby-boomers' babies. ''Yuppies want to get their kids ready for Harvard at the age of 15 months,'' says Janet Schulman, Random House juvenile division editor. ''Children's books are the fastest-growth area in publishing.'' While adult-book sales rose 4% last year, children's books zipped up 15% to $386 million at wholesale. Cashing in on the trend is a growing band of for- kids-only bookstores that lure knee-high literati by offering them dragon- drawing contests and their own charge accounts, with bills sent to Mom and Dad. While only two dozen of these specialty shops succeeded a decade ago, more than 350 now thrive across the U.S. as parents have become bigger spenders in a market once ruled by schools and libraries. Major chains have taken note: Waldenbooks has opened eight Waldenkids outlets since April and expects to add 25 more by Christmas. Barring a severe economic downturn, the outlook for kids' books is ducky. Kendrick Noble, media analyst at Paine Webber, points out that the upswing in birthrates since 1977 keeps putting more kids into the 5-to-12 age group. ''Even if no more kids were born,'' he says, ''we'd see rising sales through the first half of the 1990s.''