At the risk of sounding insensitive: an ounce of prevention is worth more than a pound of cure—this is one of those things that if it's a problem someone is experiencing, that thing is not their real problem, which is a deep failure somewhere else, way, way back.
The unvarnished truth is that the answer to your question ("how do you stop your wife and/or kids interrupting you every 30 seconds?") for many people is "I don't". They don't stop them, that is. Because they don't have to. Because they didn't marry someone who interrupts them every 30 seconds and then have kids with them and then raise those kids to be the kinds of kids who interrupts them every 30 seconds.
The unvarnished truth is that the answer to your question ("how do you stop your wife and/or kids interrupting you every 30 seconds?") for many people is "I don't". They don't stop them, that is. Because they don't have to. Because they didn't marry someone who interrupts them every 30 seconds and then have kids with them and then raise those kids to be the kinds of kids who interrupts them every 30 seconds.