Solved the problem! My bad. The issue was the child panel was set to a different layer then the rest of the GUI.
Once I changed it to the same layer that all the other NGUI elements were on then things lined up and worked as expected. Slightly surprised that when I add a panel from the NGUI menu that the resulting panel didn't inherit the layer of its parent, but not a big deal.
Thanks for the very helpful console message which I missed yesterday saying:
"You can't place widgets on a layer different than the UIPanel that manages them."
My apologies and thanks for a wonderful product! =)