This is the only way (AFAIK) to know which portal is parent or child:


Private Function GetPortalAliases(ByVal portalId As Integer) As ArrayList
        'Dim ctlPortals As New PortalController()
        Dim ctlPortalAlias As New PortalAliasController()
        Dim returnPortalAliasesList As ArrayList = New ArrayList()

        Dim portalAliasesList As ArrayList = ctlPortalAlias.GetPortalAliasArrayByPortalID(portalId) 'objPortal.PortalID)
        For Each objPortalAliasInfo As PortalAliasInfo In portalAliasesList
            Dim strPortalName As String = String.Empty
            If Convert.ToBoolean(InStr(1, objPortalAliasInfo.HTTPAlias, "/")) Then
                strPortalName = Mid(objPortalAliasInfo.HTTPAlias, InStrRev(objPortalAliasInfo.HTTPAlias, "/") + 1)
            End If
            If strPortalName <> String.Empty AndAlso System.IO.Directory.Exists(Me.SiteRootPhysicalPath & "\" & strPortalName) Then
                ' child portal, so ignore it
            Else
                ' parent, portal, so list it
                returnPortalAliasesList.Add(objPortalAliasInfo)
            End If
        Next
        Return returnPortalAliasesList
    End Function



Best,
Horacio.-