local and global state

components.child\.hbs

<div>
{{@name}} is checked: {{this.isChecked}}

</div>

<Input
  @type="checkbox"
  @checked={{this._isChecked}}
  {{on "click" (fn @onClick this._isChecked)}} />

components.child\.js

import Component from '@glimmer/component';
import { tracked } from '@glimmer/tracking';
import { action } from '@ember/object';

export default class Child extends Component {
  previousParentState;

  @tracked _isChecked;
  
  get isChecked() {
    // if (this.args.isChecked !== this.previousParentState) {
    //   this.previousParentState = this.args.isChecked;
    //   this._isChecked = this.args.isChecked;
    // }
    console.log(this.args.allChecked)
    return this._isChecked;
  }
//   previousParentState;

//   @tracked _isChecked;
  
//   get isChecked() {
//     if (this.args.isChecked !== this.previousParentState) {
//       this.previousParentState = this.args.isChecked;
//       this._isChecked = this.args.isChecked;
//     }
    
//     return this._isChecked;
//   }
}

controllers.application\.js

import Controller from '@ember/controller';
import { action } from '@ember/object';
import { tracked } from '@glimmer/tracking';

export default class ApplicationController extends Controller {
  @tracked allChecked = false;

  @action
	toggleAll(state) {
    this.allChecked = state;
  };

  @action 
	onChildClick(state) {
    if (!state == false) {
      this.allChecked = false;
    }
    return false;
  };
}

templates.application\.hbs

<div>
Parent
</div>
<Input
  @type="checkbox"
  @checked={{this.allChecked}}
  {{on "click" (fn this.toggleAll this.allChecked)}} />

<Child
  @name='child 1'
  @allChecked={{this.allChecked}}
  @onClick={{this.onChildClick}}
/>

<Child
  @name='child 2'
  @allChecked={{this.allChecked}}
  @onClick={{this.onChildClick}}
/>

<Child
  @name='child 3'
  @allChecked={{this.allChecked}}
  @onClick={{this.onChildClick}}
/>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}