ngOnInit() is executing twice

We are creating own tag for our component in that parent tag (Query group) should call child tag each grid (table) but ngOnInit() called twice in parent. The code is below:

this.source = "http://entitlements/rest/data/queryv2/page_builder_repo_ms/vw_query_group_details/";
var sample = "assets/sampleQueryGroup.json";/*For testing only ! */
this.httpClient.get(sample, { observe: 'response', params: postPayLoad }).subscribe(resp => {

  console.log('      resp.body.toStr   ' + JSON.stringify(resp.body['Response']['Rows']));
  var self = this;
  resp.body['Response']['Rows'].forEach(function (row,index){
    self.items.push(row);
  });
  console.log("  lenght  ====    "+this.items.length);
})