open a mdi child from an other child - RESOLVED

I have a mdi form on my application, and a mdi child that have a button that i want to open other form, that is also a mdi child.
i´ve tried this:

VB Code:

Dim f As New adi_clientes
        f.Parent = Me.ParentForm
        f.Show()

and

VB Code:

Dim f As New adi_clientes
        f.Parent = Me.Parent
        f.Show()

but it doesn´t work!

Anybody have some help??

Thank You,
Guilherme Costa

VB Code:

Dim f As New adi_clientes
        f.MdiParent = Me.ParentForm
        f.Show()

If both are MDIChildren then this should work also:

VB Code:

Dim f As New adi_clientes
        f.MdiParent = Me.MdiParent 
        f.Show()