Ok, remedies...

(1) some TVs have flash memory, the moment you unplug them and wait for the capacitors to clear, the TV will forget the childlock


(2) for some TVs - you need to press 3 or 4 digits to unlock - try the usual suspects and press 'ok' or 'enter'
    
     You could try 111 or 123 as 1111 and 1234 are common factory presets.
    
or  666 - number of the beast
   
or 667 - neighbor of the beast


(3) Most devices only lock the remote, so you can access the device by pressing the -/+ volume buttons on the TV front at the same time - similarly, some sets allow you to press the channel -/+ to access the device.
   
- you can also try these buttons on the TV itself