Fire brigade head Dave Brown said an elderly woman had lit the grill in the garden, and then pulled it into the kitchen to dry clothes, the BBC reported Saturday.
She then left the house, leaving her four grandchildren -- ages 10 months to 4 years -- and two daughters-in-law, ages 26 and 29, inside, authorities said. The woman left the kitchen door open, but someone then closed the door.
Two of the children were in the living room and the other two were asleep upstairs, London24 reported.
A relative later entered the house, found the grill, and took it outside. When she returned inside one of the children collapsed, and the relative called for emergency assistance.
All six people have been discharged from the hospital.