A baby has survived after plunging from a third floor window, landing on a concrete overhang around 20ft below.
The recent hot weather is believed to have led to a spate of other children also being injured after falling from open windows.
The one-year-old baby escaped with just a broken jaw after the fall in Amhurst Road, Hackney, east London.
A Metropolitan Police spokesman said officers were called just before 4pm yesterday to reports that a child was seen bleeding on a roof.
He said: "It was later established that an infant had fallen from a third floor window onto a concrete overhang, between the ground floor and first floor levels.
"A member of the public managed to climb on the overhang and get hold of the child, preventing him from falling the further distance.
"The one-year-old male infant was conveyed to an east London hospital where it was established that he had sustained a broken jaw. Injuries not deemed life-threatening or -changing."
Inquiries into the incident are ongoing, he said.
And doctors at Barts Health NHS Trust also issued a warning after four children were admitted to the Royal London Hospital in Whitechapel, east London, following similar incidents in the past 24 hours.
Alastair Wilson, a consultant at the hospital, said: "We have noticed a big rise in the number of children who have fallen out of windows during the recent hot spell.
"We would ask parents and carers to be careful and ensure children are kept well away from open windows."
Sheila Merrill, public health adviser at the Royal Society for the Prevention of Accidents (RoSPA), said parents and guardians should take measures to ensure windows were safe.
She said: "Now that the summer has arrived, windows will most likely be open for longer periods of time. Parents should consider the risks posed to their young children when opening windows.
"Consider fitting child resistant window restrictors - these limit the opening to less than 100mm but allow you to get out easily in an emergency. Avoid putting anything under the window that can easily be climbed by a child.
"Those most at risk from a home accident are the 0-4 years age group. Falls account for the majority of non-fatal accidents and the worst injuries are sustained when a child falls from a great height."