When should I make the transition from a Maxi-Cosi Group 1 seat to a Group 2/3 seat?

For the safety of your child, we recommend using the Group 1 car seat (9 months to 3 1/2 years/9-18 kg) for as long as possible. Wait to switch your child to a next stage car seat when your child has reached the maximum weight limit or if the top of your child’s head protrudes above the top edge of the seat. As long as the back of your child's head is fully supported by the shell, we advise against making the switch just yet, so that your child can be offered the best possible protection.