When your child is 2 years old or if your child is almost 2 and has outgrown the rear-facing weight or height limit of a convertible car seat or 3-in-1 car seat, your child's car seat needs to face forward. Keep using a forward-facing car seat with the harness until your child is around 4 years old and outgrows the highest weight or height allowed by the car seat's manufacturer. Secure the car seat in the back seat of your vehicle.