When it comes to how easily Junior has transitioned to school, you talk a big game.Back it up with a Crumpler backpack. Originally created for Aussie bike messengers, the kid-size bags are tough enough to withstand a good dragging down subway stairs (and a few don’t-leave-me tantrums).The Baby Pea, designed with preschoolers in mind, has comfy, padded straps that fit easily over tiny shoulders. The main zipper pocket leaves just enough room for snacks, water, and a sweater.Bigger minds (read: kindergartners) will appreciate the extra cargo space of the Baby Anchovy. Plus, a reflective strip along the base helps your little scholar say, “Watch out, world, here I come.”Wonder where he gets that from.Available at Crumpler, 45 Spring Street, at Mulberry Street (212-334-9391); 49 Eighth Avenue, between Horatio and Jane Streets (212-242-2535); online at crumplerbags.com.Photo: Courtesy of CrumplerFARMStone Barns Center’s Harvest FestWhat: A fall celebration full of delicious food, live music, and farm activities for all ages.Why: Reap what you sow.When: Sat., 10 a.m.-3 p.m.Where: Stone Barns Center for Food and Agriculture, 630 Bedford Rd., Pocantico Hills. For tickets, call 800-838-3006 or go to brownpapertickets.com.WATCHPeter and the WolfWhat: The Little Orchestra Society puts a new musical spin on Prokofiev’s classic tale.Why: Score one for the kids.When: Sat., 10:30 a.m. & noon; Sun., 1 & 2:30 p.m.Where: Gerald W. Lynch Theater at John Jay College, 899 Tenth Ave., b/t 58th & 59th Sts. For tickets, call 212-971-9500 or go here.LISTENThalia Kids’ Book Club: Judy BlumeWhat: A rare appearance by the noted children’s author gives little readers (ages 6 and up) a chance to chat about The Pain and the Great One.Why: You’ve loved her forever.When: Sun., 1 p.m.Where: Symphony Space, 2537 Broadway, at 95th St. For tickets, call 212-864-5400 or go here.