Mazda 2003 B2300 Owner's Manual page 97

The importance of shoulder belts
Using a booster without a shoulder belt increases the risk of a child's
head hitting a hard surface in a collision. For this reason, you should
never use a booster seat with a lap belt only. It is best to use a booster
seat with combination lap/shoulder belts.
WARNING: Follow all instructions provided by the
manufacturer of the booster seat.
WARNING: Never put the shoulder belt under a child's arm or
behind the back because it eliminates the protection for the
upper part of the body and may increase the risk of injury or
death in a collision.
WARNING: Never use pillows, books, or towels to boost a
child. They can slide around and increase the likelihood of
injury or death in a collision.
SAFETY SEATS FOR CHILDREN
Child and infant or child safety seats
Use a safety seat that is recommended for the size and weight of the
child. Carefully follow all of the manufacturer's instructions with the
safety seat you put in your vehicle. If you do not install and use the
safety seat properly, the child may be injured in a sudden stop or
collision.
Seating and Safety Restraints
97