(HealthDay News) -- Backpacks, if stuffed too full, can be so heavy that they can cause back pain and injury.

Here are some warning signs that your child's backpack is too heavy, courtesy of the U.S. National Safety Council:

• Your child's posture changes when the backpack is on.
• Your child has difficulty putting the backpack on, or taking it off.
• Your child has pain while the backpack is on.
• Your child feels a sensation of numbness or tingling while wearing the backpack.
• Your child has red marks on the shoulders or back from the backpack.

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