The incident took place at the Vishweshwar Temple in Chembur area of northeast Mumbai around 3.30 p.m. when the children, a boy and a girl, were walking past, said an official of Brihanmumbai Municipal Corporation's (BMC) Disaster Control Room.
The wall suddenly came crashing down on Anjali A.Mhaske, 7, and Vishal S.Vagule, 8, killing them instantly, the official said.
The cause of the collapse of the wall, on which the temple's main hoarding was fitted, is not yet known.
Their bodies were taken to the nearby Shatabdi Hospital by police even as hundreds of people gathered at the scene of the tragedy.
Police deployed tight security in Khardev Nagar area, where the temple is located, to prevent any untoward incident.