Condition 3 G21 .45 - either of my small children is FAR from being able to manipulate the action. Condition 3 Kalashnikov, same story. Other items also just in case we wake up in the process of being murdered in bed with an attacker in too close of proximity for either of us to get to a firearm, chamber it, and shoot.
Before kids it was condition 2 on the firearms. When they are bigger and have their sketchy little friends over it will be full lockdown till they are asleep, and again when they wake up.
When the kids leave I'll be old and likely condition 2/1 depending on platform
The key with most children (not all are the same) is to train them and take them shooting to remove the "mystery" so they have no reason to ever want to see or play with your secured firearms out of boredom or curiosity. Make sure they know that every gun is ALWAYS loaded so they treat it as such. This covers you when they are around 99.9999% of the time, but you always have to be extra vigilant if they have friends over.
And yep - I believe a good dog to trump any alarm system.