relay.ts

@Component({
  selector: 'child-dumb-component',
  template: `
    <button>clicky</button>
  `
})
export class ChildDumbComponent {
  @Output() customEvent = new EventEmitter();
}

@Component({
  selector: 'parent-dumb-component',
  template: `
    <child-dumb-component></child-dumb-component>
    <child-dumb-component></child-dumb-component>
  `
})
export class ParentDumbComponent {
  @Output()
  @ObserveChildren(ChildDumbComponent, 'customEvent') childEvents;
}