Adjust the harness fitA child's car seat harness should fit snugly across their body. Car seat manufacturers don't recommend using any devices that have not been crash-tested with their particular brand and model of car seat. Our car seats laboratory assessed some to check whether they would affect the protection a car seat offered, or impede a parent or emergency worker if they needed to get a child out of the car seat in a hurry. Read our guide to baby car seat accessories for our recommendations on what you should or shouldn't use to prevent your child escaping from their car seat. Remember to put the child lock on your car doorWhether your child tries to escape from their car seat or not, remember to put a child lock on the rear passenger seat doors to prevent them opening them when the vehicle is moving.