Most of those are because of bad habits learned in childhood, habits than can be prevented by education at an early age. Some manufacturers offer special child-sized versions for children ages 5 to 10. Consider more than looks when choosing a backpack. An ill-fitting pack can cause back pain, muscle strain or nerve impingement. You want to have padded shoulder straps to avoid pressure on the nerves around the armpits.
Some backpacks have waist straps designed to stabilize the load.
These should be used whenever possible. The proper maximum weight for loaded backpacks should not exceed 15 percent of the child's body weight. For example, an 80-pound child should not carry more than 12 pounds in a pack. If the pack forces the carrier to bend forward, it is overloaded. In loading, it is obvious that excessive backpack weight can cause problems.