findcontrol in child master page

I have a master page and a second master page which is a child of the first master. The child master has a control, label, I want to access in page_load of my aspx page.
Master Page: (Site.master) <%@ Master Language="C#" AutoEventWireup="true" CodeFile="Site.master.cs" Inherits="Master_Site" %> <asp:ContentPlaceHolder id="head" runat="server"></asp:ContentPlaceHolder> <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server"></asp:ContentPlaceHolder>
Child Master Page: (Compactors.master) <%@ Master Language="C#" MasterPageFile="~/Master/Site.master" AutoEventWireup="true" CodeFile="Compactors.master.cs" Inherits="Master_Compactors" %> <asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server"> <asp:ContentPlaceHolde ...