Chevrolet 2003 Silverado 1500 Pickup Owner's Manual page 40

Never do this.
Here two children are wearing the same belt.
The belt can't properly spread the impact
forces. In a crash, the two children can be
crushed together and seriously injured. A belt
must be used by only one person at a time.
I
I
Q:
What if a child is wearing a lap-shoulder belt,
but the child is so small that the shoulder belt
is very close to the child's face or neck?
A:
If the child is sitting in a rear outside seat position,
move the child toward the center of the vehicle.
See Rear Safety Belt Comfort Guides for Children
and Small Adults on page 1-29. If the child is
sitting in the center rear seat position of a crew cab,
move the child toward the safety belt buckle. In
either case be sure that the shoulder belt still is on
the child's shoulder, so that in a crash the child's
upper body would have the restraint that belts
provide.
If the child is so small that the shoulder belt is still
very close to the child's face or neck, you might
want to place the child a seat that has a lap belt, if
your vehicle has one.
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