Rear passenger side door will not open from outside or from inside...child safety lock is engaged

I had the same problem w/ my right rear door on my civic lx 1998:

My little nephew was playing with the child proof locking mechanism, so I though that was the problem, I started to take the inside door trim panel apart and using my flashlight I discover that the spring located in the door handle was a rusted, so I applied a bit of WD40 and wha-la, it work like charm (I guess all it needed was some lubrication so the spring can expand and contract in order to open the door smoothly.

For sure I will pointing the high pressure water gun from the car washes away from the door handle

I opened mine by unscrewing the internal handle and pull the metal rod manuelly .....sorted

The child safty lock may be on but that wont stop you from opening it from out side,,,, it only stops kiddys from opening it from the in side,,,
i think the lock has broken?

The child safety lock should stop the door from opening from the inside as that is it's purpose however the external door handle should open the door. It sounds as though the actuating rod has disconnected some how from the door latch mechanism. this often happens when a "slim Jim" or hanger has been used to open the door incorrectly. You will have to find a way to get the door open so this can be repaired. Your best bet is most likely to have a dealer do this as I can think of no way to access the door release parts without damaging the interior door panel with the door closed.