Some movement in the head area of rear-facing car seats is common, even when car seats are correctly installed. Follow the installation instructions for your car seat, and then test for tightness. With weakest hand at belt path, tilt and push the car seat forward and back and from side to side. Some movement from front to back or about an inch from side to side is acceptable. The vehicle belt or LATCH belt used to secure the car seat should not loosen during this test.