How to force a Server Control in asp.net to accept only one type of children?

Question

Hi, I am trying to make a server control in asp.net and force it to accept only one type of child elements. I mean something like this:

<cc:foo runat="server" ID="myCC">
    <cc:bar runat="server" ID="my2ndCC"></cc:bar>
</cc:foo>

But I want to allow only children of type bar and nothing else. Does anyone have any idea how to achieve this?

Thanks in advance.