The children died in the fire, which started just after midnight yesterday, but their mother died later at in hospital.
Two more of Ms Newell's children, Cassandra, six, and Asheley, five, were last night fighting for their lives at Guy's Hospital, south London.
Police in Southwark arrested a man in connection with the blaze.
A spokeswoman for Southwark council said they had no idea who the Newell family were. "We are aware they were visiting the tenant of the flat but we have no information about the family," she said.
Police were unsure about where Ms Newell had come from or what she was doing in the flat, which was rented to three men in August.Reuse content