parent
(integer) List those pages that have the provided single page only ID as parent. Defaults to -1 (displays all Pages regardless of parent). Note that the 'hierarchical' parameter must be set to 0 (false) -- which is not default -- or else no results will be returned for any page other than the top level pages with no parent (ID=0) and the default all pages (ID=-1). In contrast to the 'child_of' parameter, this parameter only returns the direct descendants of the parent, no 'grandchildren'. You can obviate the 'hierarchical' set to 0 requirement by passing a 'child_of' parameter set to the same (parent) ID value.
-1 - default, no parent restriction
0 - returns all top level pages