I like Neil's idea of focussing on the latter portion of the story, particularly the constancy of God and the idea that the lying and blaming are the greater faults.  However, there are some other complexities to the story that I see as good talking points that I have never seen mentioned in a Sunday school lesson:

Was it "fair" of God to lie about the repercussions of eating the fruit (or was it a lie --death of innocence, etc.)  ?  Would the same choices have been made if God had been more straightforward?

Was the choice to eat the fruit really a sin?  Like Pandora's box, you can argue that God set Adam and Eve up for failure.  Adam and Eve did get knowledge out of the deal (and being cast out of the garden also gave them independence).  Is choosing a hard life with knowledge worse than an easy life and ignorance or innocence?  Even children have to make choices that are in grey areas (like when to "tell" on someone) that might have both positive and negative results. 

The nature of myth, what questions this story answered for its original hearers and the truth about the human condition and nature of God that we can still learn from today, regardless of whether or not you see this story as a myth or literal truth.

Was greater knowledge and independent thought/action in humans God's purpose all along?  Was the purpose of the prohibition simply to ensure that Adam and Eve were "ready" for that next step?

We do work with students up to grade 12, so some of these would be concepts I would raise with our teens and not the younger students, but others would be part of the lessons for our elementary students as well.