Seaton Carew beach in Hartlepool saw two men die after entering the sea to help two children in difficulty, Cleveland Police said.
15:45 BST was when police were called; the RNLI brought both men from the water, but they were pronounced dead shortly afterward.
Two children were taken to hospital for checks and were confirmed safe.
Cleveland Police said the deaths are not being treated as suspicious, with a file to be prepared for the coroner and family liaison officers supporting relatives.