There are several situations I can think of where I'd have no issues ending someone....and feel very little guilt. If someone was trying to hurt my kids, or was between me and my kids and they were in danger....they'd be done. In most cases like that I wouldn't need to cover it up, as it would be legally not so horrible....but if I needed to cover something like that up, and it fell within my earlier parameters, sure.
Don't I sound all cold and calculating...sheesh.
I've had this discussion before, and I've had dreams where someone broke in my house and was holding my kid, and I shot them without even a moment of hesitation. I think in real life it would be similar. I have a very strong mother bear instinct.