I know that in the safe and sound seat we used to have, the 5 point harness was only safe up until 18kgs. Has that changed? Are they only going by height now? That seems crazy to me. As soon as I found out about the 18kg limit, I took ds (I think he was around 21kgs at the time) straight out of it. He would have only been 3 or 4 years old though?