Ford 2003 Mustang Owner's Manual page 95

Seating and safety restraints
Do not leave children, unreliable adults, or
pets unattended in your vehicle.
To improve the fit of lap and shoulder belts on
children who have outgrown child safety seats, Ford
recommends use of a belt-positioning booster seat
that is labelled as conforming to all Federal motor
vehicle safety standards. Belt-positioning booster
seats raise the child and provide a shorter, firmer
seating cushion that encourages safer seating
posture and better fit of lap and shoulder belts on
the child.
A belt-positioning booster should be used if the
shoulder belt rests in front of the child's face or
neck, or if the lap belt does not fit snugly on both
thighs, or if the thighs are too short to let the child
sit all the way back on the seat cushion when the
lower legs hang over the edge of the seat cushion.
You may wish to discuss the special needs of your
child with your pediatrician.
SAFETY SEATS FOR CHILDREN
95