Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
     System.EventArgs) Handles Button1.Click
        '// MDI Childs öffnen
        Dim f As New frmChild
        Me.IsMdiContainer = True
        f.MdiParent = Me
        f.Show()
        AddHandler f.Closing, AddressOf Me.frmChild_Closing
    End Sub
    Private Sub frmChild_Closing(ByVal sender As Object, ByVal e As _
      System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
        '// MDI Child Closing 
        Debug.WriteLine(sender.ToString + " geschlossen")
    End Sub