One of the things to remember as a parent who is sending a very young child off to school is that whatever they use to carry their books to and from class should be appropriate for their stature so this means children's backpacks should be tried on and measured before they're taken to school by anyone. There are many reasons why having a backpack that's too heavy is a very bad idea for children, but generally the best way to check out whether a backpack is working well or not is to check out the age recommendations on the side of the bag.