The bombardment killed a two-day-old baby in the children's hospital in a besieged eastern neighbourhood of Aleppo, said the Independent Doctor's Association, a group of Syrian doctors that supports clinics in the city.
The infant's oxygen supply was cut after a strike on the hospital at 1:00 am (2300 GMT), the second strike on the hospital in about nine hours, according to the IDA.
"The doctors could only yell for their colleagues to take cover and shield the babies," the group said in a statement.
The World Health Organisation said Syria was the most dangerous place for health care workers to operate last year, with 135 attacks on health facilities and workers in 2015.
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In recent months, several hospitals have been damaged and medical staff killed in the densely populated eastern neighbourhoods of Aleppo city.
A hospital in the eastern Maadi neighbourhood was hit just eight days ago, wounding some of the staff and patients inside.