It was ok a long time ago but not anymore

So I have a confession.  It's one the Primary would not look favorably upon but I have it nevertheless.  Here it is:  I have a really hard time teaching scripture stories to my kids.  In fact, I'd go so far as to say I've displayed signs of avoidance.  It's not that I don't want them to learn the gospel or because I'm lazy (although you could definitely make a believable argument there if you wanted). 

I've been blessed with an eldest child who is a thinker, who really wants to grasp life, and who's been in a "good guy/bad guy" phase for most of his life. (It's my fault it started as early as it did because in an attempt to be a vigilant parent I told him about kidnappers WAY too early and scared the dickens out of him for life.)  I also have a child who as much as he loves his brother, can turn on a dime if the brother wrecks his track, which is why when we put in the first Bible DVD and the story was Cain killing Abel I popped it out faster than I can run for chocolate.

So yes, I dont' like teaching scripture stories because I have a really hard time explaining when it's all right to cut off your opponents head in the Bible but not kick your brother.  When I do venture into scripture land it's usually with sanitation and ultra caution.  Last night though, in a weak moment I let one slip.  We were telling the story of David and Goliath.  I was reading the story from a paper while the kids gleefully put together a paper puzzle of Goliath and played with a little David cut out complete with stone bag.  All was going as planned until I got to the last part when I inadvertently proclaimed that David cut off Goliath's head. 

"HE CUT OFF HIS HEAD???"

I was stuck like a deer in the headlights.  I wished I could take back the last five seconds but it was too late.  The words lingered like bad smog.  Then I launched a discussion that I prayed made some sort of sense to a five year old trying to grasp right and wrong.   

I wish I knew how to better handle these sorts of discussions and how to incorporate the scriptures without making them sound hypocritical to everything else we are trying to teach them.  If you have any great insight, please share, because this one leaves me baffled by the battles and really the last thing I want is scripture reenactments from the two boys who get wild anyway.