Just saw this article...
New laws to crack down on distracted drivers

with this being the relevant bit:
The laws also make it compulsory for children to be in a child restraint until age seven. Infants must be in a capsule until six months of age
wow, just went looking cos was wondering about the convertible seats (as opposd to capsules), and found this which provides some clarification:
The national age-based changes to child restraint and booster seat rules require:
- Children less than six months to be secured in an approved, properly fastened and adjusted, rear-facing child restraint, such as an infant capsule;
- Children from six months to less than four years must be secured in an approved, properly fastened and adjusted, rear-facing child restraint or a forward-facing child restraint with an inbuilt harness; and
- Children aged from four years to less than seven years must wear an approved, properly fastened and adjusted, forward-facing child restraint with in-built harness or an approved booster seat which is properly positioned and fastened.
(source: Media Release - New national safety laws to better protect kids in cars : VicRoads)

tbh, I don't know exactly what is different to how it was before, but thought it was useful info.