Use the parent filter

frontend/app/components/api/api-v3/api-v3-filter-builder.ts

@@ -34,7 +34,7 @@ export interface ApiV3Filter {
 
 export class ApiV3FilterBuilder {
 
-  private filters:ApiV3Filter[] = [];
+  public filters:ApiV3Filter[] = [];
 
   public add(name:string, operator:FilterOperator, values:any):this {
     let newFilter:ApiV3Filter = {};

frontend/app/components/wp-relations/wp-relations-hierarchy/wp-relations-hierarchy.directive.ts

@@ -40,6 +40,12 @@ export class WorkPackageRelationsHierarchyController {
   public canModifyHierarchy = !!this.workPackage.changeParent;
   public canAddRelation = !!this.workPackage.addRelation;
 
+  public childrenQueryProps = {
+    filters: JSON.stringify([{ parent: { operator: '=', values: [this.workPackage.id] }  }]),
+    'columns[]': ['id', 'type', 'subject'],
+    showHierarchies: false
+  };
+
   constructor(protected $scope:ng.IScope,
               protected $rootScope:ng.IRootScopeService,
               protected $q:ng.IQService,

frontend/app/components/wp-relations/wp-relations-hierarchy/wp-relations-hierarchy.template.html

@@ -21,8 +21,7 @@
         </div>
     </div>
 
-    <wp-embedded-table queryId="5"
-                       [query-props]="{ 'columns[]': ['id', 'type', 'subject'], showHierarchies: false }"
+    <wp-embedded-table [query-props]="$ctrl.childrenQueryProps"
                        [configuration]="{ splitViewEnabled: false, columnMenuEnabled: false, contextMenuEnabled: false }">
     </wp-embedded-table>