Try This :
Dim V As New FrmTest
V.MdiParent = Me.MdiParent
V.Show()
The above assumes that MDIChild1.MdiParent
is already set to MDIParent1
You could also do this :
Dim V As New FrmTest
V.MdiParent = Application.OpenForms("MDIParent1")
V.Show()
To close other forms, iterate through MdiChildren
collection :
Dim MyMdiForm as Form = Application.OpenForms("MDIParent1")
For Each Frm As Form In MyMdiForm.MdiChildren
If Frm IsNot V Then
Frm.Close()
End If
Next