At what weight or height does my child need to transition from rear-facing to forward-facing mode?

Your child must transition to forward-facing mode once they exceed 18 kg (40 lbs) or 102 cm (40 in.) in height, or when the top of their head is less than 2.5 cm (1 in.) from the top of the headrest. If your child exceeds these requirements but is less than 2 years old, you must discontinue use of the car seat entirely. The American Academy of Pediatrics recommends keeping children rear-facing for as long as possible, and some states require rear-facing use until age 2. (Page 5)