My DD was almost 14 kgs at 2 and at just over 3 she has only just new passed the 18 kg mark- we had her in the 8-26 kg type and I only took the 5 point harness off a couple of weeks ago, she now has a protecta harness on there. It would really be worth checking out the changes to the child restraint laws, I am pretty sure that it is in there that they have to be in a proper 5 point harness until they reach the age OR weight limit (which ever comes first), before they can go into a booster seat.