Chances are, if the kid has access to the gun unattended, they can also find the key. Honestly, how many of you guys that use trigger locks have every single key to the lock either on you, within your sight, or outside of the house at all times? If you leave the gun and child unattended with the key in the house, you shouldn't feel secure.
Also, I don't know what kind of kids these liberals have, but the ones I've helped raise see a lock as a challenge that must be beaten. The thought of, for example, my eight year-old great-nephew, seeing something locked from him scares me. He is clever, and he will find a way around it. I've found that boring a kid with details about a gun is much more effective deterrent than telling them "guns are bad, don't touch." I tell them not to touch them, then I explain how it works and the physics behind it. Works every time. I didn't teach him to fear the gun (like a liberal would). I taught him it's something not for him and something not that interesting (yet).z