Forms Data Controls :: Passing Data Between Nested Gridview?

I have a page where there are two nested gridview, I have a column in the child gridview that uses a function to display the data.This function uses the id of the id of the father and son as parameters. I tried the code below, but does not work ...

[i]
<asp:GridView ID="gvParent" runat="server" AutoGenerateColumns="False" OnPageIndexChanging="gvParent_PageIndexChanging" AllowPaging="true" OnRowDataBound="gvParent_RowDataBound">
<Columns>
<asp:BoundField DataField="ParentId" HeaderText="ParentId"></asp:BoundField>
<asp:TemplateField HeaderText="Childrens">
<ItemTemplate>
<asp:GridView runat="server" ID="gvChildren" AutoGenerateColumns="false" OnRowDataBound="gvChildren_RowDataBound">
<Columns>
<asp:BoundField DataField="ChildId" HeaderText="ChildId"></asp:BoundField>
<asp:TemplateField HeaderText="MyFun">
<ItemTemplate>
[b]<%#MyFun(Eval("ParentId"),Eval("ChildId"))%>[/b]
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>[/i][Edit by="mtugnoli" on="18 gennaio 2011 16.29"][/Edit]