What are the legal requirements for child car seats in Perth?

All children must be safely fastened in the correct child car seat for their corresponding age and size.

Correct child car seats for children’s age and size (source)

Up to 6 months
A baby less than 6 months old must be put in an approved rearward-facing child car seat. This can be a baby capsule or a convertible child car seat.
6 months to 4 years
The minimum legal requirement for your child is an approved forward facing child seat with an inbuilt harness. However, rearward child car seats give your child the best protection
4+ years
Your child can now use a booster seat with a properly fastened and adjusted seatbelt or child harness.
145cm or taller
Your child should atleast be 145cm (or 4 feet 9 inches) to use the adult lap-sash seatbelt.