Calling Parent From Child

In my child constructor I use MovieClip(this.parent).blablabla() to retrieve info, yea I know I can pass it through the constructor, anyways I keep getting errors anytime I try to use MovieClip(this.parent) in the constructor, it gives a refrence error saying it’s null.

Why doesn’t that command work, is there a way around it (other than the constructor)? Is it because it’s bad design? I’m calling a function that has alot of data, so I’m just passing this to the child and using the passed this data to call the parent atm, looking for a better MovieClip(this.parent) solution.