i stumbled upon a common problem when parenting lately: the children are miraculously distorting when transforming (rotating). freezing transformations will fix your troubles. the following snapshot illustrates my problem:
create a simple setup with two cones and two cylinders; be sure you scale the base a bit larger, so i can illustrate a common problem. name your stuff and parent all, preferably in the hypergraph window (drag a prospective child with the middle mouse button onto the prospective parent), which is more fail-safe, especially if you named your stuff. the following order makes sense: shade, upper arm, lower arm, stand. move down the pivot points of both the arms to their base. if you didn’t scale the base like i said before you won’t encounter a problem right now since all element have the same scale values (1,1,1). but you will experience unwanted distortions when you have different scale values: rotate the lower arm and you’ll see how the upper arm and the shade are going to shear out. so the parented children inherit the scale values! freeze transformations will fix the problem: just freeze the transformations of all elements and the problem disappears since they have now all the same scale values again.