Buick 2001 Century Owner's Manual page 69

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.
Wherever the child sits, 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.
1-57