Not anymore if you are building a new house. New laws to protect children falling out of windows have come into force.
Since 1 May 2013, the Building Code of Australia (BCA) requires “protection for openable windows in new homes where the floor below the window is more than 2m above the surface beneath” (i.e. 2-storey homes).
The protection is either a device to restrict the window opening, or a screen, so a 125mm diameter sphere (representing the size of a young child’s head) cannot pass through. The device or screen must also be able to withstand an outward horizontal force of 250 N.
The picture is called “By the open window” painted by Konstantin Makovsky.