At What age does a child need to wear a PFD while the boat is underway?

In many jurisdictions, children under the age of 13 are required to wear a personal flotation device (PFD) while the boat is underway. However, specific age requirements can vary by state or country, so it's essential to check local regulations. Additionally, it's always a good practice for all passengers, especially children, to wear PFDs for safety, regardless of the legal requirements.