New Twiddle

components.checkbox-list-checkbox.js

import Ember from 'ember';

const { Checkbox, computed } = Ember;

export default Checkbox.extend({
  attributeBindings: ['checked'],
  checked: computed('checkedItemsSet', function() {
    return this.get('checkedItemsSet').has(this.get('item'));
  }),
  didInsertElement() {
  	console.log('inserted');
  },
  click(e) {
  	this.get('onClick')();
  }
});

components.checkbox-list.js

import Ember from 'ember';

const { Component, computed } = Ember;

export default Component.extend({
  checkedItemsSet: computed('checkedItems', function() {
    return new Set(this.get('checkedItems'));
  }),
  actions: {
    onCheck(item) {
      let checkedItemsSet = this.get('checkedItemsSet');
      if (checkedItemsSet.has(item)) {
        checkedItemsSet.delete(item);
      } else {
        checkedItemsSet.add(item);
      }
      this.get('onCheck')(Array.from(checkedItemsSet));
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  init() {
    this._super(...arguments);
    
  	this.set('items', [
      { firstName: 'Tom' },
      { firstName: 'Yehuda' }
    ]);
    
    this.set('checkedItems', [
    	this.get('items.lastObject')
    ]);
  },
  actions: {
    handleCheck(checkedItems) {
      console.log(checkedItems);
    	this.set('checkedItems', checkedItems);
    }
	}
});

templates.application.hbs

{{#checkbox-list
	items=items
  checkedItems=checkedItems
  onCheck=(action "handleCheck") as |list|}}
  {{list.checkbox}} {{list.item.firstName}}
{{/checkbox-list}}

templates.components.checkbox-list-checkbox.hbs

{{yield}}

templates.components.checkbox-list.hbs

{{#each items as |item|}}
  {{yield (hash
    item=item
    checkbox=(component "checkbox-list-checkbox"
      checkedItemsSet=checkedItemsSet
      item=item
      onClick=(action "onCheck" item)
    )
  )}}
{{/each}}

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"
  }
}