In this edition of The Recommendation, we share the story of the time 100 kids came to our office. Plus: their favorite backpack bling.“But … why?”This is the question I heard over and over a few weeks ago, when we invited 100 kids (yes, really) to The New York Times offices for two days of school supply testing.I heard it the most as kids tried on a series of backpacks, which we wrapped to conceal the brand and print. First, why were the backpacks so heavy? Why were the backpacks covered up? Why did they have to try on another one? Then, why were there four pounds of dried beans inside a backpack? Just about every single time a kid unzipped the pack and peered inside, they would be incredulous: “Beans?! Why?!”Well, because we wanted kids to tell us which backpacks felt the most comfortable. The beans — we had also considered bean bags and exercise weights — were meant to stand in for a typical school load.This was part of a larger, ambitious endeavor: to pick the 15 best back-to-school supplies, according to kids. For two days this summer, kids ages 6 to 10 got their hands on 80 products — from backpacks to markers, lunch boxes to glue sticks.