Won’t my child’s legs be squished? I don’t want her to be uncomfortable.
Kids are flexible. Your baby spent the last 4 months of your pregnancy tucked up into a little ball; as a newborn all he wanted was for you to swaddle him as tightly as possible, tucking his knees up as high as they'd go, to keep him calm. Your 6-month-old thinks that chewing on his feet is the best activity ever. Your toddler may no longer want to be swaddled or teethe on her toes, but I'm sure she sits in some pretty contorted positions when playing on the floor with her toys. Ever try sitting in a "W" like your toddler often does? I'll bet you haven't, because adults typically aren't flexible enough. Ever watched a 5-year-old sleep with his chin on his chest during a long car ride and think "ouch, that can't be comfortable," yet your 5-year-old amazingly wakes up happily with no complaints of a stiff neck? Kids are flexible because their joint spaces aren't fully formed; since they aren't fully formed in their knees and ankles, your rear-facing preschooler is able to sit comfortably even though they appear somewhat cramped.
Many parents also worry that it is unsafe for the child's legs to be bent in a crash. Won't they break a leg? Could their knees go into their stomach and hurt them this way? Turning to data from real kids in real crashes, we know that the answer is NO—they typically won't break their leg, and we have not seen any abdominal injuries. In fact, studies show there are many more leg injuries to forward-facing children than to rear-facing children. As a pediatrician, I worry most about the brain and spinal cord, as these are the parts of the body we don't know how to fix if they get broken. Rear-facing protects the brain and spinal cord much better than forward facing. A broken leg should be the worst injury your child has; six weeks in a cast, and they are as good as new.