But where do their legs go?!

Children can sit with their legs bent or crossed quite comfortably.

Look how children sit in Kinder/Primary school for group times. Legs crossed on the floor.

Kids are flexible, their bone structure is VERY different to adults. Adult have 206 bones vs a newborn starting out with nearly 300 bones! They have more flexible cartilage (a firm tissue softer than bone) in the body that enables more flexibility. When they grow some of the cartilage hardens and turns into bone, while some bones fuse together.

This means not only is it fine for their legs to sit in all sorts of funny ways while rear facing, but because their spine hasn't ossified their spinal cord is NOT protected from the forces of a crash if they were forward facing. Don't turn them forward just because YOU think they look uncomfortable. If they are uncomfortable you should get their seat checked as it may be that the seat needs adjusting, the harness height raised etc.

Observe how toddlers and young children squat down to pick up /play with toys.. their feet FLAT on the floor, their bum almost touching the ground (Example image above) ! Try this as an adult and we almost topple over with shin splint pain after a few seconds.

MYTH: Children will break their legs when rear facing if their feet touch the vehicle seat. FACT: Children have an increased risk of a broken leg when forward facing due to their limbs getting thrown forward with such force and often hitting the front seat.