As per the Australian law all children up to seven years old are to be correctly restrained according to their age and size.

0 - 6 months - Rearward facing infant restraint

6mts to 4yrs - Forward facing child restraint with built-in harness

4yrs to 7yrs - Booster seat with lap-sash H-harness or a booster seat with a secured adult seatbelt