“All infants and toddlers should ride in a rear-facing car safety seat (CSS) until they are 2 years of age or until they reach the highest weight or height allowed by the manufacturer of their CSS.”
The American Academy of Pediatrics recommends rear facing until a minimum of age 2, but preferably until the child reaches the rear facing height or weight limit of their seat. Ideally, a child should remain rear facing until around 4 years old.
Why? A toddler’s body is still forming as he grows. The bones have not fully ossified, and cartilage is connecting a toddler’s vertebrae rather than strong, ossified bone.
To get technical, those cartilage connections are called synchondroses, which slowly close over time. There are three major points of ossification, each with two synchondroses.
According to a study published in the Association for the Advancement of Automotive Medicine, the first station to close is the C3, second is the axis, and third is the atlas. Even by the time a child turns 3, there’s only a 50% chance that his C3 vertebra have fully ossified. The longer you can keep your child rear facing, the better the chance that his spinal column will have strengthened over time.
(photo credit: White, T. Human Osteology, 2000)
The above image shows the cervical (top), thoracic (middle), and lumbar (bottom) vertebrae of a one year old (left, each photo) and six year old (right, each photo). Note the easily visible synchondroses in each.
Another item to consider is how much weight a toddler’s spine is supporting. An average nine-month-old child’s head makes up 25% of his body weight, while an adult’s head only makes up 6% of its body weight. This difference in proportion only adds to the need to protect the spinal column.
During a crash, occupants travel towards the point of impact, putting all the stress on the neck and spine. At that moment there are actually three impacts: the vehicle striking whatever it strikes, the body of the occupant being retained by the seat belt or harness, and then the internal organs striking the front of the inside of the body. In a crash, a rear-facing car seat cradles and moves with your child, combining impacts number 2 and 3. This helps reduce stress to his fragile neck and spinal cord.
A common misconception is that once a child outgrows their “infant seat” (usually around 10-12 months of age) the next step would be to put him in a forward facing harnessed seat. However, there is actually a seat called a “convertible seat” that fills in the few years between an infant seat and a forward facing seat. Many of the convertible car seats manufactured today have higher weight and height limits, allowing them to be used in a rear facing position until age 3 or 4, and are priced as low as $45!