How officers responded to a disturbance that led to a 26-hour siege in Greater Manchester is being investigated by the police watchdog.
Police were sent to a house in Shaw, Oldham, in the early hours of 25 July amid concerns for a woman's welfare.
They later returned at 03:15 BST to reports of a man allegedly armed with a gun, holding a woman and two children hostage.
The Independent Police Complaints Commission is now investigating.
The woman, 27, and a child received injuries requiring hospital treatment, the IPCC said.
Marc Schofield, 30, was charged with false imprisonment and two counts of possession of an imitation firearm.
He is due to appear at Manchester's Minshull Street Crown Court on 25 August.
Catherine Bates, of the IPCC, said: "Our independent investigation is in its very early stages.
"We will look at the police response to the initial report of a domestic incident and the actions of officers involved in dealing with this report."