What type of seat should a 4-year-old exceed in weight if they are over 40 lbs?

A 4-year-old who exceeds 40 lbs should transition to a booster seat. This is because booster seats are designed to properly position the vehicle’s seatbelt across the child's body, ensuring that in the event of a crash, the belt fits correctly over the stronger parts of their body, such as the hips and shoulders, to minimize injury risk.

While it is true that a child could remain in a forward-facing seat or a convertible seat at this weight, these types of seats do not provide the same level of seatbelt positioning as a booster does when the child is of appropriate weight and height. Additionally, using a standard seatbelt without a booster for a child under 4 feet 9 inches tall could lead to improper restraint, which can increase the chance of injury during an accident. Thus, as children grow and exceed certain weights and heights, ensuring they are in the proper seat type is critical for their safety.