Lie. There's no duty to tell the truth when asked such a question by them.
Better to lie about it. It will go into the statistics they keep and show that there are fewer guns in existence to "save the children" from. No problem in need of a Lefty solution. If you say yes then you're giving the turds ammo to use against you later on.
There is also some merit in having a ton of statistics showing there are millions of responsible gun owners out there whose guns are not being used, stored or accessed inappropriately and no notable incidents came out of their ownership.