New Twiddle

components.child-component.js

import Ember from 'ember';

export default Ember.Component.extend({  
  click() {
    this.attrs.toggleHeight(); 
  }
});

components.parent-component-a.js

import Ember from 'ember';
export default Ember.Component.extend({
  heights: Ember.Object.create(),
  
  actions: {
    toggleHeight(item) {
      this.heights.toggleProperty(item.item);
    } 
  }
});

components.parent-component-b.js

import Ember from 'ember';

export default Ember.Component.extend();

controllers.application.js

import Ember from 'ember';

const Wrapper = Em.Object.extend({
  checked: Ember.computed.alias('state.checked')
});

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  items: Ember.A(['red', 'blue', 'green']),
  states: {},
  
  decoratedItems: Ember.computed.map('items', function(item) {
    let state = this.states[item];
    state || (state = this.states[item] = Ember.Object.create());
    return Wrapper.create({ item, state });
  }),
  actions: {
   addItem() {
      this.get('items').addObject('yellow');
    },
    removeItem() {
			this.get('items').removeObject('yellow');    
  	},
  	toggleChecked(item) {
      this.get('decoratedItems').findBy('item', item).toggleProperty('checked');
    },
    changeItem() {
      this.get('items').replace(0, 1, 'orange')
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<button {{action 'addItem'}}>Add item</button>
<button {{action 'removeItem'}}>Remove item</button>
<button {{action 'changeItem'}}>Change item</button>
{{items.firstObject}}
{{parent-component-a items=decoratedItems toggleChecked=(action "toggleChecked")}}
<hr/>
{{parent-component-b items=decoratedItems toggleChecked=(action "toggleChecked")}}
<br>
<br>

templates.components.child-component.hbs

<li style="background-color: {{if heightToggled 'red' 'white'}}">
<input type="checkbox" 
       checked={{item.checked}} 
       onclick={{action toggleChecked item.item}} />
  {{item.item}}
</li>

templates.components.parent-component-a.hbs

{{#each items as |item|}}
	{{child-component item=item toggleChecked=toggleChecked heightToggled=(get heights item.item) toggleHeight=(action 'toggleHeight' item)}}
{{/each}}

templates.components.parent-component-b.hbs

{{#each items as |item|}}
	{{child-component item=item toggleChecked=toggleChecked}}
{{/each}}

twiddle.json

{
  "version": "0.7.2",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.4.4",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.4.3/ember-data.js",
    "ember-template-compiler": "2.4.4"
  }
}