which children have to wear a seatbelt or child restraint?

In Australia, the law is as clear as a sunny day: all children under 7 years old must be secured in an appropriate child restraint or booster seat. Once they hit 7, it's seatbelt city, but only if the seatbelt fits properly (usually when they're tall enough to sit with their back against the seat and feet on the floor). If not, the booster seat sticks around like an unwelcome guest at the party. Failure to comply can lead to fines and demerit points, because the authorities take child safety as seriously as a kangaroo takes a hop.

To sum up, children under 7 must use child restraints, and from 7 onwards, it’s seatbelt time—unless they're too small, then the restraint stays. Always check the latest official documentation for any state-specific nuances.