Hi Phill,
If you just check the box for show child page site map in "Page Settings", then it will be on top. But there is an alternate way to add a child page site map to the page just like other features by choosing Child Page Site Map from the list in "Edit This Page" as IndigoTea indicated. Doing it that way allows you to position it just like any other content feature. You can put it below or even in a side column.
Hope that helps,
Joe