Two other children and a woman were already out of the house before emergency services arrived. They were checked over by ambulance staff but did not need hospital treatment.
West Midlands Police said officers had cordoned off the scene as they work to establish the exact circumstances of the fire.
Det Ch Insp Kylie Westlake described the deaths as a “truly tragic incident”.
“Our thoughts remain very much with those who loved the children who have been lost,” she said.
“We understand the shock and distress this awful incident will have caused to many people and we are working at pace to ascertain exactly what has happened.
“While we would ask people not to speculate about this or the wider incident, we would ask that anyone who can help with our enquiries, and who is yet to speak with us, to get in contact.”
