Private Sub Command1_Click()
   Dim oForm As NEW Form1
   oForm.Picture1.Visible = True
   Unload Me
End Sub

Option Explicit
Private childs_form1 As New Collection
 
Private Sub mnuCreateChild_Click()
      Dim newf1 As Form1
      Set newf1 = CreateChild
      newf1.Show
End Sub
 
Private Sub mnuDeleteChild_Click()
    If childs_form1.Count = 0 Then Exit Sub
 
    Dim IDstr As String
    Dim ids() As Integer, Index As Integer
    ids = GetIDs
    For Index = 1 To UBound(ids)
       IDstr = IDstr & (CStr(ids(Index)) & "  ")
    Next Index
 
    Dim t As String
    t = InputBox("Child-IDs: " & IDstr & vbCrLf & _
    "Welche ID gelöscht werden?")
    If t = "" Then Exit Sub
    On Error Resume Next
    DeleteChild CInt(t)
End Sub
 
Public Function CreateChild() As Form1
    Static perm_index As Integer
    perm_index = perm_index + 1
    Dim f As New Form1
    f.Tag = perm_index
    childs_form1.Add f
    Set CreateChild = f
End Function
 
Public Function GetChild(ByVal ID As Integer) As Form1
    Dim found As Boolean, f As Form1
    For Each f In childs_form1
        If CInt(f.Tag) = ID Then Set GetChild = f: Exit For
    Next f
End Function
 
Public Function DeleteChild(ByVal ID As Integer)
   Dim Index As Integer, f As Form1
   For Index = 1 To childs_form1.Count
       Set f = childs_form1(Index)
       If CInt(f.Tag) = ID Then
          childs_form1.Remove Index
          Unload f: Exit For
       End If
   Next Index
End Function
 
Public Function GetIDs() As Integer()
    Dim ids() As Integer
    ReDim ids(childs_form1.Count) As Integer
    Dim Index As Integer, f As Form
    For Index = 1 To childs_form1.Count
        Set f = childs_form1(Index)
        ids(Index) = CInt(f.Tag)
    Next Index
    GetIDs = ids
End Function

Dim f1 As Form1
Dim ids() As Integer: ids = MDIForm1.GetIDs
Set f1 = MDIForm1.GetChild(ids(1))
f1.Picture1.Visible = False

 
Private Sub Form_Unload(Cancel As Integer)
    Dim ID As Integer
    ID = CInt(Me.Tag)
    MDIForm1.DeleteChild ID
End Sub