Posting this after following a suggestion from Tim.
The widget to show pages on the front page needs to refer to a page with child pages defined.
I want to have widget sized images that link to:
a stand alone contact page,
an existing site page,
and to an external site.
I created a dummy page – called it frontpage.
Installed the plugin “redirect” – This uses a custom field called redirect, where you can enter the target URL.
I made the stand-alone page a child of the frontpage dummy page.
I created a new page, made it a child of the frontpage dummy page, set the featured image to that of the destination site page, set the redirect custom field to the URL of the real site page.
I then created a new page, gave it a featured image of the external site, set the redirect field to an offsite link and made it a child page of frontpage.
I configured the themeloom show pages widget to use my dummy “frontpage”.
Result, widget size images on the front page that link to existing, stand-alone or external sites.