How do you set the source of a treelist to be relative to the current item?

Trying to set a treelist field to only allow selection of child items of the current item. Tried a few queries that I found online but none seem to work correctly:

For example: query:./*

That works correctly in XPath Builder to show all items under the current one but when the treelist field shows up in Content Editor it only gives me the option of selecting the first child item and does not show the rest.

Anyone know what the Source needs to be to accomplish this? This is in Sitecore 7.2 but having a solution to target older versions would be nice too.