ARLINGTON, Va. -

The Insurance Institute for Highway Safety released its list of top rated booster seats on Thursday.

The ratings assess how well boosters raise kids up so that safety belts, designed for adults, fit them properly.

[READ: Booster seat report]

19 of 31 new models for 2013 earned the top rating of "Best Bet."

Surprisingly three high-end Britax models didn't earn the top rating this year because of a redesign that produces poor lap belt fit in some vehicles.

Eleven new models are rated as "Check fit," meaning they will provide proper belt fit in some but not all vehicles and that's the key. The goal is to achieve a proper fit in all vehicles so if a family moves the seat from one vehicle to another, safety will not be compromised.

The IIHS says proper fit is when the bottom belt rests flat across the upper thighs and not over the stomach. The upper belt should be snug across the center of the shoulder not sliding off or riding up on the neck.

The group stresses parents shouldn't be in a rush to move kids into booster seats from a traditional forward facing restraint in the back seat. They should wait and reach the limits of the height and weight restrictions.