polymorphism with created_at and modified_at

Hi,

I was wondering what happens, if I use polymorphism in combination
with created_at and modified_at?

Lets say I have 3 models, which all have the attributes created_at and
modified_at, then how will they updated?

Will changes in the child affect the "modified_at" of the parent?

Will a "child.attribute_at()" yields the value of the child or the
parent?

Given the child, how can I read the attribute of the parent?

Fritz