GMC Yukon Denali 2003 Owner's Manual page 55

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CAUTION:
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.
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 seat outside position,
move the child toward the center of the vehicle.
See Rear Safety Belt Comfort Guides for Children
and Small Adults on page 1-44 . If the child is
sitting in the center position, 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.
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