A mother and child, who were rescued from the sea yesterday, have died in hospital.
A third child is missing, feared dead in Scarborough's North Bay, say police.
A huge air-and-sea search was launched just after 4pm after the mother and her two children and another adult were swept into the sea off the North Yorkshire coastal resort.
The tragic news came as a search continued for a father and 13-year-old daughter who went missing from a boat at around 3pm on Loch Lomond in Scotland.
The girl's 15-year-old sister raised the alarm after she was discovered in the rubber dinghy by two anglers.
Humber Coastguard reported that it received numerous emergency calls at around 4pm reporting two adults and two children had been swept into the water.
A spokesman said that an 11-year-old boy had been swept into the water and the rest of his family had gone in to try and save him.
The family got into difficulty and were being swept out to sea although one, a male adult, managed to get ashore.
Humber Coastguard launched a search-and-rescue mission, with a rescue helicopter from Leconfield which was in the air at the time getting to the scene at Scarborough within eight minutes.
Coastguard rescue teams from Scarborough, Filey, and Burniston were called out to mount a shoreline search, and the Scarborough Lifeboat was requested to launch.
The rescue helicopter recovered the 11-year-old boy and his 33-year-old mother and took them to hospital, but they were later pronounced dead.
Drew Mahood, Humber Coastguard Watch Manager, said it was difficult to carry on the search after darkness last night.
"Our sympathies go out to the family and friends at this tragic time." The missing 13-year-old is the dead woman's daughter.
Police said the sea was not particularly rough, but it was extremely cold.
