In an accident if a child is forward facing the only thing holding in the body is the harness. The child's head flies forward and it can cause injuries to the head, neck, and spinal cord. As Angela mentioned, yes there is something called internal decapitation, and it does happen. It is when the head becomes detached from the spinal column. The spinal column can stretch up to 2 inches, but the spinal cord can only strech 1/4 in before it snaps.
If a child is RF in an accident, the back of the seat cradles their head and neck, preventing it from whipping forward. It also contains the entire body reducing arm and leg injuries.
I know it looks strange when a RF toddler's legs are curled up or crossed, and at a first glance it looks like it might be dangerous, but it's perfectly safe. There have been no documented injuries to the legs because of rear facing. And even if there was a broken leg can be repaired, a broken neck cannot.
Here are some links with a little more info.The Importance of Rear Facing
- a short video explaining well, the importance of rear facingSacred Journeys - Rear Facing Rocks
- a great site with lots of good info and linksJoel's Journey
- warning, this is about a child who broke his neck in a car accidentRF Crash Test
vs. Forward Facing Crash Test
- actual crash test footageRear Facing Photo Album
- this shows pictures of older children rear facing