This question has been answered by garybiltmore. See the first response.
do you want to show us your complete call?
<span> [[!If? &subject=`[[+isfolder]]` &operator=`EQ` &operand=`1` &then=` <div> <input id="inner[[+parent]][[+idx]]" type="checkbox" name="inner[[+parent]][[+idx]]"> <label for="inner[[+parent]][[+idx]]">[[+pagetitle]] - [[+idx]]</label> <div class="drop"> [[!getResources? &parents=`[[+id]]` &limit=`0` &tpl=`sidebar-nav-dropdown.tpl` &includeContent=`1`]] </div> </li> </div> ` &else=`<a href="[[~[[+id]]]]">[[+pagetitle]]</a>` ]] </span>
[[!getResources:default=`<a href="[[~[[+id]]]]">[[+pagetitle]]</a>`? &parents=`[[+id]]` &limit=`0` &tpl=`sidebar-nav-dropdown.tpl` &includeContent=`1`]]
I would do this the other way around. Have the getResources snippet, with a default for when no children are found.How does that call know if a resource is a parent or not?
[[!getResources:default=`<a href="[[~[[+id]]]]">[[+pagetitle]]</a>`? &parents=`[[+id]]` &limit=`0` &tpl=`sidebar-nav-dropdown.tpl` &includeContent=`1`]]
[[!getResources@myPropertySet]]
<div> <input id="inner[[+parent]][[+idx]]" type="checkbox" name="inner[[+parent]][[+idx]]"> <label for="inner[[+parent]][[+idx]]">[[+pagetitle]] - [[+idx]]</label> <div class="drop"> [[getResources? &parents=`[[+id]]` &limit=`0` &tpl=`sidebar-nav-dropdown.tpl` &includeContent=`1`]] </div> </li> </div>
<a href="[[~[[+id]]]]">[[+pagetitle]]</a>
&tplCondition=`isfolder` &conditionalTpls=`{"1":"folderTpl","0":"nonefolderTpl"}` &tpl=`nonefolderTpl`