As of now, “The Academy [of pediatrics] continues to recommend that all children ride in a rear-facing car safety seat as long as possible, up to the manufacturer’s stated weight and length limits.” Many seats on the market nowadays will accommodate children rear facing to at least 4 years old, and even beyond that. So keep those kiddos rear facing up to the limits and make sure those seats are installed correctly! Below are some photos of my son (always off the charts for height and weight) rear facing at 4 years old. Hopefully these serve as a good illustration that big kids are safe rear facing and bent legs are not a safety concern!
Full update from American Academy of Pediatrics: http://pediatrics.aappublications.org/content/early/2018/08/28/peds.2018-2460
Kristen Sanders is a Child Passenger Safety Technician Instructor and owner of Buckle up, Bumblebee; a mobile service that offers private car seat checks and educational classes for families of all backgrounds. You can contact her at www.buckleupbumblebee.com or Kristen@buckleupbumblebee.com