Recent changes to booster-seat laws in Kentucky, Massachusetts and Michigan expose the hodgepodge of state rules that govern the use of car safety seats by children older than four.

The states are uniform in their requirement that children use a car seat until they outgrow front-facing child restraints, usually around the age of four and 40 pounds. But at that age and size kids are still too small to ride safely using only the vehicle's seats belts, which are constructed to fit adults. Booster seats elevate children to a height where they can wear the car's belts correctly.

Not every state has a booster seat law. And even states that have passed laws fail to agree on what age, size or weight a child should be to graduate from a child restraint to car seat belts.

With such a variety of state laws, it's hard for a parent to know what to do. Learn more in our Safety blog.

See our car seats section and car-seat timeline for more information.