The chest clip is a pre-crash positioning device, meaning it does its most important duty before a vehicle crash occurs. The clip, when used properly, keeps the car seat harness in the right place against the child's shoulders, so that crash forces are distributed over the strongest parts of the child's upper body.
I have spoken with more than one parent who mentioned that, after a crash, they noticed that the chest clip of their child's car seat was bent or broken. This does not mean that the car seat did not do its job during a crash. As long as the chest clip keeps the shoulder portion of the harness in the right place until a crash occurs, it has performed adequately.
The chest clip of your child's car seat should always be fastened and positioned at the child's armpit level. If the chest clip is positioned too low, such as over the child's stomach, the shoulder straps of the harness can slip down from the child's shoulders, leaving the child inadequately protected in a crash.
Heather Corley is a certified Child Passenger Safety Technician and Senior Checker with Safe Kids USA.