Jane Brody:

Dr. Ari Brown – pediatrician in Austin, Tex., spokeswoman for the American Academy of Pediatrics and author of “Baby 411: Clear Answers and Smart Advice for Your Baby’s First Year” – cautions that in haste to get children the clothes and supplies they need for school, health issues are sometimes overlooked.
She and other experts offer the following advice:
BACKPACKS Many children have no lockers in school and are forced to carry all their books back and forth to school and between classes. An overweight pack can cause muscle strains and overuse injuries and distort the child’s posture.
A loaded backpack should not weigh more than one-fifth of a child’s weight. The pack’s shoulder straps should be wide and padded on the back as well. The pack should always be carried using both straps. “Now and then, a parent should check what’s in the pack and determine if everything has to be carried daily,” Dr. Brown suggested.