What is the longest distance swim for a child?

As of my last knowledge update in October 2021, the longest distance swim by a child was achieved by Thomas Gregory, who swam 36 kilometers (22.4 miles) in 2014 at the age of 12. However, records may have changed since then, so it's advisable to check the latest updates from official swimming organizations or record-keeping bodies like Guinness World Records for the most current information.