New Twiddle

components.child-component.component.js

export default Ember.Component.extend({
  click: function() {

  this.set('regChildCount', this.get('regChildCount') + 1);

  this.attrs.mutChildCount.update(this.attrs.mutChildCount.value + 1);
    this.attrs.mutChildCount.update(this.attrs.mutChildCount.value + 1);
    
  this.attrs.mixChildCount.value = this.attrs.mixChildCount.value + 1;
  }
});

components.child-component.template.hbs

mut: {{mutChildCount}}<br/>
reg: {{regChildCount}}<br/>
mix: {{mixChildCount}}

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  
  controllerCount: 0
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1><br><br>
ctlr: {{controllerCount}}

{{child-component 
  regChildCount=controllerCount 
  mutChildCount=(mut controllerCount)
  mixChildCount=(mut controllerCount)}}