I have a webform

I have a custom control on my webform

I am trying to find a dropdown list control inside of the custom control by using the following code but it's not working:
cType(FindControl("ddlMyDropDownList"), DropDownList).SelectedValue

How can I find a control that is inside of a custom control or how do I find a control that is in another webform and be able to use their values / text / etc?

Thank you in advance.