New Twiddle

components.x-wizard-step.js

import Ember from 'ember';

export default Ember.Component.extend({
  init() {
    this._super(...arguments);
    this.get('register')(this);
  },
  
  willDestroyElement() {
    this._super(...arguments);
    this.get('unregister')(this);
  }
});

components.x-wizard.js

import Ember from 'ember';

const { computed } = Ember;

export default Ember.Component.extend({
  children: computed(function() {
    return [];
  }),
  childCount: computed('children.[]', function() {
    return this.get('children.length');
  }),
  actions: {
    registerChild(child) {
      this.get('children').pushObject(child);
    },
    unregisterChild(child) {
      this.get('children').removeObject(child);
    }                               
  }
});

controllers.application.js

import Ember from 'ember';

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{#x-wizard as |wizard|}}
  {{#wizard.step}}
    step1
  {{/wizard.step}}
  {{#wizard.step}}
    step 2
  {{/wizard.step}}
{{/x-wizard}}
<br>
<br>

templates.components.x-wizard-step.hbs

<h2>Wizard-step</h2>
{{yield}}

templates.components.x-wizard.hbs

Child-count: {{childCount}}

{{yield (hash
  step=(component 'x-wizard-step' register=(action 'registerChild') unregister=(action 'unregisterChild'))
)}}

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}