keeping track of new additions to your scene

[Andrew]

Say I have a racetrack and different types of cars that get swapped in and
out on a mousedown action. Is there a way to store ONLY the new models (and
their children) in a list so that I may later dispose of just these and
ignore the track components?

I'm trying to swap objects in and out of a scene and am getting quite
frustrated with not being able to get rid of models that have been cloned
into the scene without having child objects and other resources staying in
memory.