It would help to know the model number of your oven. Then we could look it up in the
Panasonic Operating Instructions online.
Not knowing your model number, I selected model #NN-MX26 at random. The instructions for that model state:
The Child Safety Lock prevents the electronic operation of the oven until cancelled. It does not lock the door.
TO SET: Press Stop/Reset three (3) times. CHILD appears in the display window. CHILD continues to be displayed until Child Lock is cancelled. Keypads can be pressed but the microwave will not start.
TO CANCEL: Press Stop/Reset three (3) times. The display will return to colon or time of day when Child Lock has been cancelled.
NOTE: You can set Child Lock feature when the display shows a colon or time of day.