Use ItemChild and NextSiblingItem properties to scan the collection of child items. 

The following sample shows how to scan recursively all child items hosted by an item:

Sub RecItem(ByVal g As EXPLORERTREELibCtl.Group, ByVal h As EXPLORERTREELibCtl.HITEM)
    If Not (h = 0) Then
        Dim hChild As HITEM
        With g.Items
            Debug.Print .CellCaption(h, 0)
            hChild = .ItemChild(h)
            While Not (hChild = 0)
                RecItem g, hChild
                hChild = .NextSiblingItem(hChild)
            Wend
        End With
    End If
End Sub