Use a forward-facing car seat correctly in a back seat every time your toddler rides in a car.
Use the right car seat with a harness for your toddler's weight and height. Toddlers are weighed and measured at every doctor visit, so be sure to keep track.
Use the car's safety belt or LATCH system to lock the car seat into the car. Your car seat should not move more than one inch side to side or front to back. Grab the car seat at the safety belt path or LATCH path to test it.
Put harnesses through the slots so they are even with or above the child's shoulders. Some seats require use of the top slots when the seat is forward-facing, so check instructions.
Be sure the harness is tight, so you can't pinch extra webbing at the shoulder.
Use a top tether if your vehicle and car seat are both so equipped. Tethers limit the forward motion of your child's head in a crash. If you don't have them, contact your car dealer and car seat manufacturer.
Adjust the chest clip to armpit level.
A child is too big for the seat when the shoulders are above the top slots, the tops of the ears are above the back of the seat or the weight limit is exceeded. Move to a taller car seat or a booster seat. Many children will outgrow the harness of a forward-facing car seat at age 4 or 5.
Be sure all occupants wear safety belts correctly every time. Children learn from adult role models.