A: There is a point at which using a toddler booster seat with the 5-point internal harness is no longer considered safe and it’s based on your child’s weight.
Toddler booster seats with an internal harness are for toddlers 20 to 40 pounds. (For seat specs, check the owner’s manual of the seat you buy.) Some toddler-boosters can be used with the seat’s own harness for weights up to 65 or even as high as 80 pounds, for kids who are heavier than average for their age. But if the toddler booster seat you buy can’t be used that way, it’s time to trade-up to a belt-positioning booster seat when your child reaches the seat’s weight limit.
A belt-positioning booster seat is generally for children weighing 40 to 100 pounds. It uses only the vehicle’s own safety belts to restrain your child, but it’s designed to correctly position both the lap and shoulder portions of the vehicle’s belt correctly across the stronger parts of a child’s body, the collarbone and hip area.