In a moment of inattention she veered into the path of a pickup truck. She died of massive head injuries. She wasn't wearing a helmet. Her grieving parents hope that this photo will bring home how much every parent has to lose. Replace any helmet when your child crashes in it.
Impact crushes some of the foam.
The helmet is less protective although the damage may not be readily visible. Helmets soften impact, so the child may not even be aware that their head hit until you examine the helmet for damage. Replace the buckle if it cracks or if any piece of it breaks off. Nobody prompts you to replace your child's helmet, so give it some thought. The ASTM standards for biking and inline skating are identical, so a bike helmet can easily double as a skating helmet for normal inline skating.