As sakeneko noted, pax's website pretty much has this covered. The short answer is that if kids are around, guns need to be either securely locked up or on your person in a secure holster. I don't think there's really any middle ground, as far as that goes.
The backup to this, of course, is "Teach your children well." Teach them safe gun handling -- for younger kids, maybe all, that should include the understanding that "safe handling" means not handling them at all without an adult present. And letting them handle them with supervision, and shoot them when they're old enough, is probably a good way of demystifying guns, removing the "forbidden fruit" attraction that comes from being told "don't touch." If they know they can handle them if they ask, they may be less likely to "sneak."
But.. they're kids, and kids do stupid things, which is why locking them up (the guns, not the kids
) is also essential.
(ETA: KingEdward, ya nailed it. Fine job, and your daughter's a lucky girl to have a dad like you.)
It's newsworthy when kids take the parent's gun and shoot it. We just had an incident in the last week or two.
Parents do stupid things, too, and so do boyfriends, like the one in my area who left his gun in the girlfriend's nightstand, where her kid found it, with tragic results.
On the bb gun thing, some kid around here shot my car with a bb gun, and seems to also be killing pigeons. I'd hope kids with bb guns are supervised.[Vanya's emphasis]
I hope you called the police. In a lot of cities it's illegal to let off firearms within the city limits, and BB guns are often considered to be firearms under those laws. Shooting at cars is discouraged pretty well everywhere, I think, and killing pigeons
might be a violation of humane laws... even though they're basically rats with wings.