My larger 4.75yo son needed a new backpack for his outdoor classes and camps coming up. He was using his 7L mini Fjallraven, which has been great for preschool for the past few years, enough for a little lunch and a water bottle. But it wasn't large enough for his winter outdoor class. The Jet 12 can carry a lunch, another layer of clothes in the big pocket, plus little pockets for sunblock, sunglasses, magnifying glass, gloves, etc. We something to fill the hydration sleeve, which frees up space for everything else. The fit is perfect and highly adjustable, he's about 3'4" and 42lbs. We've only had it a short time, so I can't say anything about wear over time, but he wore it all day yesterday and it moved with him easily, something that will make his outdoor class and camps that much easier. What a great product. I'm not looking into an Osprey as a school bag for kindergarten later this year.