The four were playing on the ice at Babbs Mill Park when the ice broke. Rescuers rushed to the scene and provided first aid.
The children were then taken to two hospitals. All four allegedly suffered cardiac arrest due to hypothermia from the cold water. They are artificially ventilated.
Two missing
According to witnesses, six children aged around eleven played on the ice. The police are still looking for the other two, but assume that they too, if they really fell through the ice, did not survive the accident.
It has been cold in Britain for days and there is still a lot of freezing cold to come. Temperatures of minus 15 degrees are forecast for next week in north-east Scotland.