Unload Record Oops

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

controllers.index.js

import Ember from 'ember';

export default Ember.Controller.extend({
  actions: {
    removeChild() {
       this.model.get('children.firstObject').unloadRecord()
    }
  }
});

models.child.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  parent: belongsTo('parent')
});

models.parent.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  children: hasMany('child')
});

routes.index.js

import Ember from 'ember';

export default Ember.Route.extend({
  
  model() {
      const p1 = this.store.createRecord('parent', {
        id: 'p1'
      });
    
      const c1 = this.store.createRecord('child', {
        id: 'c1',
        parent: p1
      });
    
      const c2 = this.store.createRecord('child', {
        id: 'c2',
        parent: p1
      });

    return p1;
  }
  
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.index.hbs

<div>
Has {{model.children.length}} children
</div>
<button {{action 'removeChild'}}>Remove child</button>

twiddle.json

{
  "version": "0.13.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}