Three children were killed when an unstable wall collapsed in a building that their families had been occupying in Johannesburg's inner city, City of Johannesburg Emergency Management Services said on Monday.The incident happened between 12:00 and 13:00 on Monday.EMS spokesperson, Robert Mulaudzi said: "We are here in Doornfontein, in the inner city of Johannesburg. A wall collapsed and in the process... three children between the ages of three and 10 lost their lives.""It is an abandoned building and the walls are unstable. We are trying to remove the other unstable walls so that [they do] not collapse."Mulaudzi said Gauteng police were investigating the incident.