The boys, aged 7 and 9-years-old, were swimming in the sunshine at Sätra beach in southern Stockholm when they ran into trouble.
Their grandmother was keeping an eye on them from the beach and jumped in the water at around 3pm when she saw that they needed help.
“There was a grandmother who was there swimming with her grandchildren. Something went wrong and she went in to save the children, but died herself,” said Towe Hägg at Stockholm police.
According to witness reports, the woman managed to pull one of her grandchildren to safety on the beach.
The second child, aged 7, was dragged from the water by other swimmers, but the 68-year-old remained in the water and despite attempts to save her life she died.
The 7-year-old was rushed to Astrid Lindgren’s children’s hospital in Solna in an ambulance but later died from his injuries.
“The boy was put in a respirator during the night but it wasn’t possible to save him,” said Linda Feldt at Stockholm police to the Aftonbladet daily.
The newspaper reported that the beach was busy at the time and many people were left shocked by the events.
The police are treating the incident as a tragic accident and don’t suspect that any crime has been committed.