This story originally appeared in  Kids Today , Vox’s newsletter about kids, for everyone.  Sign up here for future editions . The Scholastic Book Fair is a big deal at my older kid’s school. A couple of times a year, the auditorium gets transformed into a kid-friendly bookstore, and the elementary-schoolers get out of their regular classes to shop for their favorite titles — just like many millennial and Gen Z readers remember from our youth . This time around, my kid was excited to come home with Buffalo Fluffalo , a bestselling picture book about a self-important buffalo who gets cut down to size. But the real must-have item on my 7-year-old’s list was not a book at all, but this furry capybara diary . The fur journal (I am trying to make a portmanteau here and failing) is a nationwide sensation, consistently one of the most popular items at book fairs, according to Laura Lundgren, chief marketing officer for the children’s book group at Scholastic.…