Watch route-children?

I have a watcher that opens a expantion item when a route is active. Can i get the watcher to react to the children as well? Or do i have to add the path for each subpage?

watch: {
 $route: function() {
      if (this.$route.path === "/page1") {
            this.$refs.page1expantion.show();
            } else  {
          this.$refs.page1expantion.hide();
        }
      }
   }


Router
        {
            path: '/page1',
            children: 
                [
                 {path: /page1/subpage1}
                ]
Page1 only have <router-view></router-view>