Well, no offense Amsdorf, but if you're not extending an invite to them because of something you know or have heard about how psycho the mommy is, that's one thing, and perhaps prudent. But if you only what-if'd yourself into not going by to invite them having no other knowledge beside just meeting the kids...you could be over-reacting to the situation and perhaps missing a great opportunity to gain new friends and to get to introduce some kids to guns.
You never know when one thing you may say to someone may stick and help them immensely later on. What-if (LOL) the parents are not gunnies but let the kids go with you, you teach them the four rules of safety and two weeks from now the kids encounter a gun in their friends house and don't pick it up and point it at their friend because of the seed you planted in their head about safety? You could potentially save a life in this fashion. There's no safety in ignorance, and every little bit helps.
If the mommy is over the hill type obvious when she answers the door, you can always drop back and punt by telling her that you're there concerned for the kids because they came up asking if they could hold the gun (your words) so you thought she should know so that she can instruct them that it is a bad thing for them to do. ???