title: Angular - use custom preloadingStrategy in forChild routes
body: <p>I have app-routing.module with one lazy loaded module which loaded dashbord.</p>
  
  <pre><code>{ path: '', redirectTo: '', pathMatch: 'full'},
  { path: '', component: AppComponent },
  { path: 'dir', 
    loadChildren: './dboard/dboard.module#DboardModule'}, 
  { path: '**', component: NotfoundComponent }
  </code></pre>
  
  <p>In dashBoardRouting I have other lazy loaded modules:</p>
  
  <pre><code>const routes: Routes = [
       {  path: '', component: DboardComponent,
          children: [             
          { path: 'accounter', 
            loadChildren: './accounter/accounter.module#AccounterModule' },
          { path: 'manager', 
            loadChildren: './maanger/manager.module#ManagerModule' },
           ...
  @NgModule({
    imports: [RouterModule.forChild(routes)],
    exports: [RouterModule]
  })
  </code></pre>
  
  <p>AccounterModule and other lazy loaded modules have their own routing modules.</p>
  
  <p>I want to use custom preloading strategy in forChild method is it possible?</p>