The force said Greater Manchester Fire and Rescue was continuing to investigate the fire, which happened at about 02:30 BST, and were “in regular contact with officers”.
Det Insp Lee Gridley said it was “a devastating incident and all of our thoughts are with the family of this young boy, who had his entire life ahead of him”.
“Together with the earlier death, this is a tragedy for the Wigan community and I know that many people will be shocked by this heartbreaking news,” he said.
“I hope people will join us in sending their absolute best wishes to all those involved… as they begin their journey in the healing process.”
He added that while the blaze was not being treated as suspicious, “if anyone has any information they believe is important, please do get in touch with us”.
A force representative said the family had asked for “their privacy as they come to terms with their loss, and have asked for people to respect their grieving process”.
