The time to transition your child out of a booster seat and into a seat belt usually comes when the child is between 8 and 12 years old. Keep your children in booster seats until they outgrow the size limits of the booster seats or are big enough to fit properly in seat belts.
And remember, always check your child's belt fit in every vehicle. A booster seat may be needed in some vehicles and not in others. If the seat belt does not fit properly yet, the child should continue to use a booster seat.