When selecting children of and object and the Binding to Parent Skeleton, two new (and duplicated) tracks are added to each object.
Here i have a video showing the simplest way i know to bind objects to another (like eyes to a head), just for you to check my steps that i'm sure are ok.
Now, suppose you have a head with two binded eyes. Now you add a hat, or multiple objects to the head. I you use the same procedure i use (selecting children and then binding them to a parent's bone) the the eyes will end up with 6 tracks: 2 originals (useless now), 2 for the first steps, and 2 more for the second step.
Regarding to my example, you may say: "don't select the eyes again". But suppose my skeleton has changed and the bones are different now. Then the eyes should be re disposed.