These locks are intended to help prevent children from accidentally opening the rear doors. Use them on both rear doors whenever a child rides in the rear seat of the vehicle.
If you slide the child safety lock to the lock position before closing that door, the door cannot be opened from the inside. The door can only be opened by pulling the outside handle.

Locking, Unlocking with Door- Lock Knob
Trunk LidMazda 6 Owners Manual: Base removal
1. Remove the rearview mirror.
2. Wind each end of a wire around a bar.
Warning
Using a SST (piano wire) with bare hands can cause injury. Always
wear gloves when using a SST (piano wire).
Note
Use a long sawing action to spread the work over the whole length
of the SST (piano w ...
Mazda 6 Owners Manual: If You Must Use the Front Seat for Children
If you cannot put all children in the rear seat, at least put the smallest children
in the rear and be sure the largest child up front uses the shoulder belt over the
shoulder.
NEVER put a rear-facing child-restraint system on the front passenger seat whether
your vehicle is equipped with a o ...