Parent Component

parent.component.html

<div style="text-align:center">
  <h1>
    Welcome to {{ title }}!
  </h1>
  <label >Parent Component Input: </label>
  <input type="text" [(ngModel)]="textInput">
  <p>Child Value is: {{childValue}}</p>
  <app-child [parentInput]="textInput" (childOutput)="updatedChildValue($event)"></app-child>
</div> 

parent.component.ts

import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  textInput = '';
  childValue = '';
  title = 'app';

  public updatedChildValue(value: string){
    this.childValue = value;
  }
}