DAze... if you're worried about little ones... and dont want to chamber load, take advantage of the built in "safe" lock on most (or all?) shotguns.
empty the chamber and magazine.
Cycle the bolt, leave it closed with an empty chamber, set the safety.
Now load the magazine.
What you have is:
A: Turn safety off to pull the trigger
B: Chamber is not loaded
C: Can't cycle the bolt w/o pressing the lever in front of the trigger to allow it to cycle w/o having pulled the trigger...
So, while its not as safe as a trigger lock, its rather complicated for a child to work their way through to both chamber a round and turn off the safety, and its faster than a lock for you because you can simple press the button and cycle a round and drop the safety in a matter of seconds, as opposed to finding a key for the trigger lock.