import { Subject } from 'rxjs/Subject';

shared-service.ts

import { Observable } from 'rxjs/Observable';
import { Injectable } from '@angular/core';
import { Subject } from 'rxjs/Subject';
@Injectable()
export class SharedService {
    // Observable string sources
    private emitChangeSource = new Subject<any>();
    // Observable string streams
    changeEmitted$ = this.emitChangeSource.asObservable();
    // Service message commands
    emitChange(change: any) {
        this.emitChangeSource.next(change);
    }
}

Now inject the instance of the above service in the constructor of both the parent and child component.

The child component will be emitting a change every time the onClick() method is called

child.component.ts

import { Component} from '@angular/core';
@Component({
    templateUrl: 'child.html',
    styleUrls: ['child.scss']
})
export class ChildComponent {
    constructor(
        private _sharedService: SharedService
    ) { }

onClick(){
  this._sharedService.emitChange('Data from child');

 }
}

The parent component shall receive that change. To do so,capture the subscription inside the parent's constructor.

parent.component.ts

import { Component} from '@angular/core';
@Component({
    templateUrl: 'parent.html',
    styleUrls: ['parent.scss']
})
export class ParentComponent {
    constructor(
        private _sharedService: SharedService
    ) {
          _sharedService.changeEmitted$.subscribe(
        text => {
            console.log(text);
        });
      }

}

Hope this helps :)