(CNN) -- Many parents are making big mistakes when using car seats for their kids.
A survey by the National Highway Traffic Safety Administration, or NHTSA, found 20 percent of parents admitted they don't read instruction manuals for installing safety seats.
NHTSA says the biggest mistakes they found were related to using the wrong slots for seat belts, or leaving the seats too loose.
But they also found about 90 percent of parents were confident their kids were buckled in safely.
NHTSA officials say traffic crashes are the number-one killer of children age one to 12.