They were in a property in Clarence Avenue, Bridlington, East Yorkshire, Humberside Fire and Rescue Service said.
Fire crews and police were called to the cul-de-sac around midnight on Thursday. The children's mother, named by police as 27- year-old Samantha Hudson, was also taken from the house.
She is in a critical condition in hospital in Scarborough, North Yorkshire.
Sources said the children were aged three, five and nine.
Superintendent Mike Duggleby, of Humberside Police, said: "Police, Fire Service and forensic experts are investigating the cause of the fire. I can say that we believe the fire started within the house and there is nothing to indicate that it was started deliberately."
This morning the three-storey terrace property was cordoned off with police tape as forensic experts examined the scene.
Nurse Lesley Salisbury (59) described how she helped perform first aid on the youngsters.
She said she ran out in her dressing gown after she was woken in the night, but first thought smoke filling the street was fog.
She said: "I saw flames coming from the bottom of the house and I ran out. To be honest, I just can't remember getting from my house to there. But a firefighter brought out a little boy.
"I told him I was a nurse and I started to work on him. I think I just went into nurse mode.
"After that it was just a blur, a dreadful blur. Some of the neighbours said I worked on the other two as well, but I don't really remember. I do remember the firefighters bringing them out, they were like little rag dolls."
Mark Rhodes, of Humberside Fire and Rescue Service, described the tragedy as "probably the most difficult, most challenging type of incident that we can ever be expected to deal with". He said: "The extent of the fire damage is considerable, the property was very heavily smoke-clogged when fire crews arrived."
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Written by Belfast Telegraph
Courtesy of YellowBrix - YellowBrix