A 23-year-old woman has been arrested on suspicion of neglect after a two-year-old boy fell from a second-storey flat window.
Police were called to Aadams Apartments, in Frog Island, Leicester, by East Midlands Ambulance Service at 16:49 BST on Saturday.
They said the child was taken to hospital with injuries not believed to be life-threatening or life-changing.
The force has appealed for anybody with information to make contact with them.
Leicestershire Police said the woman remained in custody and officers continued to investigate at the scene.
Det Insp Mike Chandler said: "We have been speaking with a number of people following the incident as we continue to establish the full circumstances regarding what has happened."