A spokeswoman for London Ambulance Service said: "We were called just before 12.40 today to reports of an incident in Eltham High Street, and sent one crew.
"Our staff treated a baby boy who had been taken unwell, who was taken to Queen Elizabeth Hospital, Woolwich."
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Temperatures soared to 27.9C in Northolt shortly after midday on Thursday, making it the warmest April day for 69 years.
The South East will enjoy the best of the weather and along with Paris will be the hottest place in Europe.
The Foreign Secretary insisted police had to "come down like a ton of bricks" on gang leaders as he warned against "going soft".