You don't want the harness of your car seat so tight that it's squishing your child, but you definitely don't want it too loose either! To get the correct tightness for a child in a harnessing seat, use the pinch test. If you can easily pinch the harness webbing at the child's shoulders, it's too loose! Your fingers should be able to easily slip off the harness while trying to pinch. Sometimes it helps if you pull up the slack from the hip area first, and then tighten the harness at the shoulders.