>
>When I set this property, I want to set all its inner controls Enabled property to the passed value.

You can iterate over the Controls collection to do this.

>Also can I have this as a static method in our public static class? If yes, what should I pass to this method?

Sure. You could pass in either a UserControl, or a ControlCollection.

public static void SetEnabled(ControlCollection cc, bool enabled)
{
    foreach (Control control in cc)
    {
        WebControl webControl = control as WebControl;
        if (webControl != null)
            webControl.Enabled = enabled;
    }
}

This isn't recursive, but should point you in the right direction.