Toyota Prius Owner's Manual page 186

1-8. Safety information
After installing the child restraint system, rock it back and forth to
ensure that it is installed securely.
Forward-facing Child seat

STEP 1
STEP 2
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If your child restraint system is
not equipped with a lock-off (a
seat belt locking feature), secure
the child restraint system using a
locking clip. (P. 190)
Adjust the head restraint to the
upmost position.
Place the child restraint system
on the seat facing the front of the
vehicle.