I don't think showing them a normal curve is a very good idea at all. It does not represent them as a part of their immediate peers and community at all, and it exaggerates the rarity of the high scores.
Assuming my family is similar to yours, then our children, as relatively affluent children of highly educated parents are going to be surrounded by relatives, family friends and classmates who are largely affluent and educated - these correlate with higher IQs. I doubt any of my friends children have an IQ much below 120 or 130. The real balance of the curve, the people with IQs below 70, are not going to be in your children's classes. And for a PG, their counterpart at the other end of the bell curve with an IQ of 55 would not even be at a public school (I assume, don't know that much about special ed).
But the kid you're showing that bell curve to doesn't understand that and would get an inflated sense of their own brilliance.
this pic illustrates it better than my words do
http://1.bp.blogspot.com/_NTpL_Vt8y...iAbNLCBA/s1600/100622+IQs+compared+2.JPG
