Which of the following indicates when to replace a child safety seat?

The indication to replace a child safety seat due to involvement in a significant crash is based on safety standards and research that show that seats can suffer structural damage that may not be visible. In a significant crash, even if the seat appears undamaged, it could have compromised its integrity and may not provide the necessary protection in future accidents. This guideline is reinforced by manufacturers' recommendations and safety organizations, which emphasize that after any crash meeting defined thresholds, a seat should be replaced to ensure optimal safety for the child.

While it is also important to consider other factors like the child's growth and the condition of the seat, those elements do not inherently compromise the seat’s ability to protect as effectively as exposure to a crash can. Therefore, replacing a seat after a significant crash is a clear and necessary guideline designed to maintain child passenger safety.