angular - how to do an Angular2 Master Detail with firebase -

im getting error : caused by: this.todoservice.getkidsdetails(...).subscribe not function typeerror: this.todoservice.getkidsdetails(...).subscribe not function

here's routing here detailinfocomponent master detail component

import {    modulewithproviders  }  '@angular/core';  import {    routes, routermodule  }  '@angular/router';    import {    workerscomponent  }  './components/workers/workers.component'  import {    admincomponent  }  './components/admin/admin.component'  import {    kidsprofcomponent  }  './components/kidsprof/kidsprof.component'  import {    homecomponent  }  './components/home/home.component';  import {    appcomponent  }  './app.component'  import {    contentmanagercomponent  }  './components/content-manager/content-manager.component'  import {    detailinfocomponent  }  './components/detailinfo/detailinfo.component'  const approuts: routes = [      {      path: '',      component: homecomponent    }, {      path: 'kidsprof',      component: kidsprofcomponent    },      {      path: 'detail/:id',      component: detailinfocomponent    }    ]    export  const routing: modulewithproviders = routermodule.forroot(approuts)

here's kids component id routings

  ngoninit() {      let id = this._route.snapshot.params['id'];      this.kidservice.getkidsdetails(id)        .subscribe(kid => this.kid = kid);      console.log(this.kid);      }

service gets firebase data specific kid

  public getkidsdetails(id) {      return firebase.database().ref('kids/' + id).once('value');    }

try on extracting route params , using them in kidservice.

ngoninit(){    this._route.params      .map(params => params['id'])      .subscribe((id) => {        this.kidservice.getkidsdetails(id)          .subscribe(kid => {             this.kid = kid);             console.log(this.kid);              }          })      });  } 

and

public getkidsdetails(id) {         return firebase.database().ref('kids/' + id).once('value')              .map(response => response.json());       }