Half of the vehicle booster seats parents rely on to keep their young children safe don't provide a proper fit with safety belts, according to the Insurance Institute for Highway Safety.

A half dozen popular booster seats proved so unsafe in testing that the IIHS specifically says to avoid them all together.

It is a frustrating day for parents reading the IIHS findings today. Conscientious parents have for years been trying to follow the recommendations of traffic safety and police, which say to keep a child in a booster seat until they are 4 foot, 9 inches tall. To find out so many of the booster seats they have been buying are inadequate to the task is a slap in the face.

Of 83 seats tested in the IIHS's fourth annual ranking, 41 got a "check fit" rating, which means that parents should check the fit of the belt each time a child straps in to make sure the belt is lying flat across a child's upper thighs and the shoulder belt crosses snugly over the middle of the shoulder. Thirty-one boosters were rated "best bets" or "good bets" by the IIHS for their design that makes it unnecessary for parents to check the fit each time.

Four booster seats made by Evenflo and two of Costco's Safety 1st brand were rated so poorly the IIHS recommended consumers not even use them: the Evenflo Chase, Express, Generations 65 and Sightseer models and Safety 1st's All-in-One and Omega Elite.

Mixed news on boosters

While the number of boosters cited for poor performance, it is worth noting that a record number of booster seats got the top rating from IIHS for their ability to properly secure children in cars. The booster seats were rated based on how well they fit 4- to 8-year-olds with the lap and shoulder belts in a wide range of vehicles.

It is interesting how different news organizations are explaining the findings, perhaps confusing consumers. USA Today's headline is "Half of Child Booster Seats Pose Risk," while Forbes.com's headline is "Booster Seats Better Than Ever." Both are technically true, but what the different takes on the news highlights is the need for parents to check the ratings themselves.

The IIHS ratings are based on how well each booster seat positions the lap and shoulder belt, its main function, and are not an assessment or rating of crash performance or vehicle fit.
If seat belts aren't positioned properly in the worst ranked seats in this year's ranking, said the IIHS, children can hit parts of the vehicle in a crash and even be injured by the belts, which can damage internal organs.

When seatbelts hit a child in the wrong place, it can cause serious internal bleeding in even a slow-speed accident.

Canada rules in boosters

The company that fared the best in the IIHS ratings was Canada-based Harmony Juvenile Products, which had all five of its seats rated "Best Bets." The first inflatable booster seat, the Bubblebum, also got a top rating.

What makes a "Best Bet" on the list? "A Best Bet means any of the top-rated boosters should work well in the family SUV or the baby-sitter's sedan," says Ann McCartt, the IIHS's senior vice president for research.

The more adaptable the booster design, the easier it is to use. According to the National Highway Traffic Safety Administration, 80% of child restraints overall, including child safety seats generally used or children from new born to four years, are used incorrectly. Most Highway Patrol offices offer free checks to make sure you are using the correct child safety seat and have it properly installed.

At the age of four, a child can move from a car-seat to a booster seat. They should remain in a booster until they are eight years old or four feet, nine inches tall. A booster seat puts a child at a height where the seat belt fits them properly.

2011 IIHS Booster Evaluation Results

Best Bets

Britax Frontier 85
Britax Frontier 85 SICT
Britax Parkway SGL (highback mode)
BubbleBum
Chicco KeyFit Strada (highback mode)
Clek Oobr (highback mode)
Cosco Pronto (highback mode)
Cybex Solution X-Fix
Diono/Sunshine Kids Monterey (highback mode)
Eddie Bauer Auto Booster (highback mode)
Evenflo Big Kid Amp
Evenflo Big Kid Sport (backless mode)
Evenflo Maestro
Evenflo Symphony 65 e3
Ferrari Dreamway SP (highback mode)
Graco Argos 70 (highback mode)
Graco TurboBooster-Baldwin (highback mode)
Graco TurboBooster Elite (highback mode)
Harmony Cruz Youth Booster/Harmony Carpooler
Harmony Dreamtime (backless mode)
Harmony Dreamtime (highback mode)
Harmony Olympian/Secure Comfort Deluxe
Harmony Youth Booster Seat
Kids Embrace Dale Earnhardt Jr. Maxi-Cosi Rodi XR (highback mode)
Recaro ProBOOSTER
Recaro ProSPORT
Recaro Vivo
Safety 1st Boost Air Protect (highback mode)
Safety 1st S1 Rümi Air The First Years B570 Pathway

Good Bets
Britax Parkway SG (highback mode)
Combi Kobuk Air Thru (backless mode)
Combi Kobuk Air Thru (highback mode)
Evenflo Symphony 65 Maxi-Cosi Rodi (highback mode)
Maxi-Cosi Rodi (highback mode)

NOT RECOMMENDED
Evenflo Chase
Evenflo Express
Evenflo Generations 65
Evenflo Sightseer
Safety 1st All-in-One
Safety 1st Alpha Omega Elite

Note: Another 41 boosters are designated "check fit." They may provide adequate belt fit for some kids in some vehicles. Go here for full list of model numbers and booster pictures.