A four-month-old baby is being treated in hospital for severe bruising and fractures.
The little girl was admitted to the Ulster Hospital in Belfast two weeks ago after being taken into Accident and Emergency by members of her family.
Social workers have become involved, but the South Eastern Trust said there were no previous files on the child, who comes from the Newtownards area.
Police are investigating.
A PSNI spokeswoman said: "Police are investigating an incident involving a four-month-old baby in the Ards area.
"Inquiries are ongoing and we have no further details."
A spokeswoman for the South Eastern Health and Social Care Trust would make no comment.
"I can confirm that we have a baby. As it is under investigation the trust is unable to make any further comment."