New Renaults have electronic child locks which also operates the rear window lock. I find that it is a better system than the one on the doors as i can turn it on and off from the drivers seat if i want to let people out.
This is what the owners manual for the Lag II says about those with out the switch.
To make it impossible for the rear doors
to be opened from the inside, move
lever 4 on each door and check from
the inside that the doors are securely
If you don't have the manual for yours then go to www.renault.co.uk
and register with my renault and you will be able to down load a manual.
In fact this is what the scenic manual says to do if you don't have the switch behind the window switches
Locking the doors manually
To make it impossible for the rear
doors to be opened from the
inside, move lever 2 on each door
and check from the inside that the
doors are securely locked.