Well, it's relative you know?
think about what valid is, or what valid means really.
say one person cannot see red.
and you present violet color, to a normal person and to this person.
normal person will see violet, that's her "valid" color
but this person will see blue only, that's her "valid"
so each of us, have our preferred truths, beliefs.
even though beliefs are not infinite in numbers, we can choose different sets, unique sets.
(and more over, we also attribute to them, different importances too)
so, it's not about the parent, or child, or whom ever.
it's about your beliefs, your point of view,
you can present your point of view, yeah
but this doesnt imply that the recipient (your parent in this case) will also accept it as truth, or will even listen to you :D
even if your parent listens, and realizes what you believe in, this doesnt mean she will also approve :D
that's the parent right, as a person, the person has the right to choose to believe whatever the person wants to believe.
so, if you actually meant "how i can convince the parent",
then it's not possible, it never is.
if you meant really "how i present my point of view"
then it's nice and dandy
as long as you don't try to impose your point of view and start a war for it