Custom field problem

I’m trying to create a page that lists the name and link to each of its child pages along with a custom thumbnail image for each.

I created a custom field in each of the child pages called “Thumbmail” and have a URL entered in there.

I think use this code:
http://pastebin.com/r39edWmn

The names of the child pages output fine and the links work, but the images do not. If you look at the source code, this is what is outputted: <img src=”” width=”80″ height=”80″>.

Any ideas why?