The shooting incident in Milton Keynes has prompted a mandatory referral to the policing watchdog.
A seriously injured child has been taken to hospital after being discovered at a Milton Keynes property where a man was found dead and another died after police fired gun shots.
Thames Valley Police officers were called to Denmead, Two Mile Ash, on Saturday over a “serious disturbance”.
They found a man in his 30s, who was later confirmed dead, and the child.
A man in his 20s was also at the property and a Taser was deployed before shots were fired, police said.
Police said that first aid was given and ambulance crews treated the man they had shot, but he was later pronounced dead.
That has prompted a mandatory referral to the the Independent Office for Police Conduct, which will carry out an investigation into police actions in the incident.
Police have not revealed any more details about the child, such as an age or whether it was a boy or girl that was found.
The next of kin of both of the dead men have been notified, police said,
Assistant Chief Constable Christian Bunt said: “What has happened can only be described as absolutely tragic and will no doubt have an impact on the community.
“Our thoughts are with those who have been impacted by this incident.”
Police are not currently seeking anyone else in relation to the investigation.
Anyone with information has been asked to contact police.