How to call a method of a child page from the main page?

On my website, most of the page stores something in the bank and for this

I define methods for each page to keep their own values

After the first release, I decided to use a unique button for saving for each page and a delete button on the page (something like a container form in Win-App). therefore I define button in master-pagefor this. but

How to call a method of a child page from the main page?

You know, the method is different from each other. I think in order to define a "virtual method", call it in the button-click event and override this on the page, butpage cs not inheritance from master-page !!!

So what should I do ?