When should a forward-facing child switch to using a booster seat?

A child should be BOTH AT LEAST 3-4 years old AND AT LEAST 40 pounds before starting to use a booster seat.

The 5-point harness of a forward-facing car seat provides optimal protection for toddlers, as it not only restricts movement, ensuring that they are in the proper position should a crash occur, but also distributes the crash forces over a larger area of the body when compared to a safety belt and booster seat (two chest straps with the safety seat versus one chest strap with the safety belt.) While many booster seats say that they can be used for children weighing more than 30-33 pounds, it is best to wait until the child is at least 40 pounds before using a booster seat.

If your over 40-pound child is not mature enough to sit still while using a booster seat (i.e. he leans over to fight with a sibling, picks up dropped toys, hangs out the window, etc.,), then he his not ready for a booster seat. In this case you should look for a safety seat that has a 5-point harness and can accomdate a child weighing more than 40 pounds.