A Lincolnshire Police update at 11.20am read: "Our officers were called to an address in High Holme Road at 8.29pm on Monday 31 May after being informed by our colleagues in the ambulance service.
"Sadly, a 26-year-old woman and her nine-year-old son, were confirmed to have died.
"Both victims suffered multiple stab wounds and a knife believed to have been used to inflict the injuries was recovered at the scene.
"Following this incident, which we are treating as murder, Lincolnshire Police launched an appeal to locate and arrest Daniel Boulton, aged 29, in connection with this incident."
Lincolnshire Police’s Head of Crime, Detective Chief Superintendent Andy Cox, said: “We are urgently seeking assistance to locate and arrest Daniel Boulton.
"Please, do not approach him as he could be potentially dangerous.
“We are not looking for anyone else in connection with this incident at present. Boulton and the victims were known to each other. No one else was injured at the property.
"However, another young child was located at the property and was uninjured.
"We understand there is speculation that was child was abducted. This was not the case and the child has been safeguarded.”
If you have seen Daniel Boulton, call 999 immediately. If you can assist with the investigation, call 101 and quote incident number 445 of May 31.