A new study shows some booster seats may not position children properly in their seat belts. A review of booster seats conducted by insurance institute for highway safety and the university of michigan transportation research institute found that 13 booster seats don't put children in the best position to be protected in a crash. The study shows the 13 seats listed may increase restraint use by making children more comfortable, but they don't position belts for optimal protection." however, experts say parents should not interpret the evaluations to mean that poorly rated seats are not effective. The federal government recommends car seats for children up to 40 pounds and booster seats for children over 40 pounds until they are eight years old or four feet, nine inches tall.