A man has been arrested on suspicion of murdering his partner and son.
Police said the 34-year-old man was known to the six-year-old boy and his mother, who was 41. They were both stabbed to death.
Officers were called to an address in Bolton-le-Sands, Lancashire, at 11.40am on Tuesday where they found the bodies of the woman and child.
The murder suspect was also at the scene at the house in Lowlands Road and had suffered stab wounds.
He was arrested on suspicion of murder and was airlifted to the Royal Preston Hospital where his conditioned is described as serious.
A cordon is in place at the scene and post-mortem examinations will take place later, police said.
Detective Superintendent Paul Withers, who is leading the investigation, said: "We are still in the very early stages of this investigation but we are conducting a number of inquiries in order to establish the exact circumstances surrounding the deaths.
"This is being treated as a murder inquiry. If anybody has any information which they believe could assist our
investigation I would urge them to contact police."
Anybody with any information should contact police on 101 or Crimestoppers anonymously on 0800 555 111 or on-line at Crimestoppers-uk.org.