Validating user control

Hi,
I have created a user control which has 4 child controls, and each of these has a requiredfieldvalidator.  The user will be able to load up to ten of these user controls onto a page.
I can validate each control with a button placed within the control, but I cannot find a way to validate all controls from a button placed on the main page.  I tried creating a public method called validate within the user control, and when called it in turn calls Page.Validate();  This isn't working (perhaps because each user control is being placed in a PlaceHolder which in turn is inside an AJAX update panel).
Can anyone point me in the direction of the best way to validate these controls?
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