Parsing visual elements inside Content Control : View Model issue

Question

I want a clean solution to a little problem i have : i have a standard main page view and its view model, inside the view i display a user control (Dossier) with its view model (DossierViewModel).

To dynamically instantiate my view from the main viewmodel i used a DataTemplate and a ContentControl :

<Window.Resources>
    <DataTemplate DataType="{x:Type vm:DossierViewModel}">
        <local:Dossier />
    </DataTemplate>
</Window.Resources>
...
<ContentControl x:Name="ContentControl" Content="{Binding SampleDossier}"/>

No problem here.

But, i have a main function which parses everything in my window in order to persist certain visual elements states. And when i use the TreeHelper to get the children of my ContentControl, i get only one, the view model DossierViewModel. Whereas what i want is the visual elements of my usercontrol binded on this view model.

How can i jump that gap ?