How to find all child controls from a starting control or form

I created a couple of extension methods that allow my program to find all of the controls from either a form or a containing control. This code is targeted for .NET 4 Client, but should also work in .NET 3.5.

Module WinformControlExtensions
  ''' <summary>
  ''' Recursively find all child controls for a form
  ''' </summary>
  ''' <param name="StartingContainer"><c><seealso cref="System.Windows.Forms.Form">Form
  ''' </seealso></c> that is the starting container to check for children.</param>
  ''' <returns><c><seealso cref="List(Of System.Windows.Forms.Control)">List(Of Control)
  ''' </seealso></c> that contains a reference to all child controls.</returns>
  ''' <remarks>If you put this module in a separate namespace from your form, Visual Studio 
  ''' 2010 does not recognize the extension to the form.</remarks>
  <System.Runtime.CompilerServices.Extension()>
  Public Function FindAllChildren(ByRef StartingContainer As System.Windows.Forms.Form) 
                  As List(Of System.Windows.Forms.Control)
    Dim Children As New List(Of System.Windows.Forms.Control)

    Dim oControl As System.Windows.Forms.Control
    For Each oControl In StartingContainer.Controls
      Children.Add(oControl)
      If oControl.HasChildren Then
        Children.AddRange(oControl.FindAllChildren())
      End If
    Next

    Return Children
  End Function
  ''' <summary>
  ''' Recursively find all child controls for a control
  ''' </summary>
  ''' <param name="StartingContainer"><c><seealso cref="System.Windows.Forms.Control">Control
  ''' </seealso></c> that is the starting container to check for children.</param>
  ''' <returns><c><seealso cref="List(Of System.Windows.Forms.Control)">List(Of Control)
  ''' </seealso></c> that contains a reference to all child controls.</returns>
  ''' <remarks></remarks>
  <System.Runtime.CompilerServices.Extension()>
  Public Function FindAllChildren(ByRef StartingContainer As System.Windows.Forms.Control) 
                  As List(Of System.Windows.Forms.Control)
    Dim Children As New List(Of System.Windows.Forms.Control)

    If StartingContainer.HasChildren = False Then
      Return Nothing
    Else
      Dim oControl As System.Windows.Forms.Control
      For Each oControl In StartingContainer.Controls
        Children.Add(oControl)
        If oControl.HasChildren Then
          Children.AddRange(oControl.FindAllChildren())
        End If
      Next
    End If

    Return Children
  End Function
End Module 

An example usage from a groupbox:

Dim oList As List(Of Control) = GroupBox1.FindAllChildren()