Obviously it depends on the age of the kid, but something up high and discrete wouldn't be all that intrusive.
I'd agree that it wouldn't be a great idea to have something they could potentially get into when they're at that exploratory age, but I think some of you are underestimating how disinterested kids can be too. If it's not presented as something exciting and it's been there for awhile, it would probably just fade into the background.
But, regardless, I would think you'd want a more child proof lock than the traditional 4-wheel luggage lock. Something with a fingerprint scanner that you could wire into the the house would be about ideal.
I do get why people are uneasy about the idea though. Kids getting a hold of guns and unintentionally shooting themselves or their friends is a pretty regular occurrence. So, keeping a gun in your kids room does - at face value - seem kind of like tempting fate. There are safe ways it could be managed, but it flies in the face of the basic "keep away from children" mantra.
si vis pacem para bellum