Buick Lucerne 2007 Owner's Manual page 45

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.
45