You cant "include" something on the same file you "extend" without wrapping it in a section. You should do this:
@extends('layouts._head')
@section('addcss')
{{ HTML::style('asset/assets/bootstrap-datepicker/css/datepicker.css') }}
{{ HTML::style('asset/assets/bootstrap-daterangepicker/daterangepicker-bs3.css') }}
{{ HTML::style('asset/assets/bootstrap-datetimepicker/css/datetimepicker.css') }}
@stop
@section('header')
@include('layouts._header')
@stop
then in your .heads file put the yield of 'header' at the very bottom (or wherever you want it)
....
@yield('header')
</html>
Or if the file remains the same in all views - just do this in .heads
....
@include('layouts._header')
</html>