Provincial police say a 10-year-old girl and her seven-year-old brother have drowned in a swimming incident at Port Burwell.
Emergency crews were called to the main beach just before 4 p.m. Friday after receiving reports that three youths had gone missing in the water.
One person was rescued and conscious, while the two others were pulled from the water and transported to Victoria Hospital in London by air ambulance in serious condition.
Police say both children were pronounced dead in hospital on Friday evening.
They've been identified as a brother and sister from Glen Meyer, in Norfolk County.
Their names have not been released.
Police say the main beach in Port Burwell was extremely busy at the time of the incident and the investigation into what happened is in its early stages.