My sister emailed the RTA and when they replied she forwarded it to me. According to what they say the laws havent changed.

A child should be in a child seat until 18kg or until its shoulders are 25mm above the highest seat belt slot or if their eye level is higher then the top of the child seat. They should then be in a booster until they meet the weight requirements of the chosen booster. They suggest most child seats will hold are child until they are 4-4.5 years of age (however my daughter out grew her child seat at 3 years by height not weight so its a rough age figure.)