Final answer:
Children should transition to a forward-facing booster seat typically at 2 years old, considering both local guidelines and the specific height and weight recommendations of the booster seat.
Step-by-step explanation:
When transitioning children from a rear-facing car seat to a forward-facing booster seat, the recommended age is typically 2 years old, which corresponds to option b). This is because children ages 0 to 2.5 years are better protected in a rear-facing car seat due to the support it provides to their head, neck, and spine in the event of a collision. By the age of 2, most children have developed enough physically to safely switch to a forward-facing booster seat. However, it is important to check both the height and weight recommendations of the booster seat you are considering, as well as local laws and guidelines, which can vary.