Reload child component when variables on parent component changes. Angular2

Question

I have a MasterComponent which loads header, footer, sidebar etc. On the header there is a dropdown whose options are set once the user is logged in. I want the header to be

Answer 1

update of @Vladimir Tolstikov's answer

Create a Child Component that use ngOnChanges.

ChildComponent.ts::

import { Component, OnChanges, Input } from '@angular/core';
import { ActivatedRoute } from '@angular/router';

@Component({
  selector: 'child',
  templateUrl: 'child.component.html',
})

export class ChildComponent implements OnChanges {
  @Input() child_id;

  constructor(private route: ActivatedRoute) { }

  ngOnChanges() {
    // create header using child_id
    console.log(this.child_id);
  }
}

now use it in MasterComponent's template and pass data to ChildComponent like: