ember init two-way-binding works as expected

components.child-component.js

import Ember from 'ember';

export default Ember.Component.extend({
    didReceiveAttrs() {
        this._super(...arguments);

        if (this.get('name') === undefined) {
            this.set('name', 'tom');
        }
    }
});

components.parent-component.js

import Ember from 'ember';

export default Ember.Component.extend({
    	surname: 'dale',
      actions: {
        myAction() {
            console.log(this.get('name'));
            this.set('surname', 'davis');
        }
    }
});

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>
{{parent-component}}
<br>
<br>

templates.components.child-component.hbs

{{name}}
<br>
{{surname}}

templates.components.parent-component.hbs

{{child-component name=name surname=surname}}
<button {{action "myAction"}}>Change Surname</button>

<br>
Below is parent's own name; it will be updated after change surname button is clicked due to two-way-binding working at didReceiveAttrs after child re-rendering!
<br>
<b>{{name}}</b>

twiddle.json

{
  "version": "0.8.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.5.1",
    "ember-data": "2.5.2",
    "ember-template-compiler": "2.5.1"
  }
}