Pontiac 2003 Vibe - Manual (Page 62)

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CAUTION:
Never do this.
Here a child is sitting in a seat that has a
lap
- shoulder belt, but the shoulder part is behind
the child. If the child wears the belt in this way, in
a crash the child might slide under the belt. The
belt’s force would then be applied right on the
child’s abdomen. That could cause serious or
fatal injuries.
The lap portion of the belt should be worn low and snug
on the hips, just touching the child’s thighs. This applies
belt force to the child’s pelvic bones in a crash.