Having trouble executing the user id session after user logs in

Here is the following codes i have so far for the sign up page login page and homepage. note i am only posting the php I know everything is working except for the user id session. I am connected to my database and row 1 is id and is the primary key.

here is the signup php

<?php
require ("func/insert.php");

if(isset($_POST['Submit']))
    {
        $first_name = mysqli_real_escape_string($con, $_POST ['first_name']);
        $last_name= mysqli_real_escape_string($con, $_POST ['last_name']);
        $email= mysqli_real_escape_string($con, $_POST ['email']);
        $password= $_POST ['password'];

        $StorePassword= password_hash($password, PASSWORD_BCRYPT, array('cost' => 10));

        $sql = $con->query("INSERT INTO users ( first_name, last_name, email, password)
                    VALUES ( ' {$first_name} ' , ' {$last_name} ' , ' {$email} ' , ' {$StorePassword} ' )");
        header('Location: login.php');
    }
?>

HEre is the login php

<?php require ("func/insert.php"); ?>
<?php
    if(isset($_POST['Login']))
    {
    $email= mysqli_real_escape_string(htmlentities($con, $_POST ['email']));
    $password= mysqli_real_escape_string(htmlentities($con, $_POST ['password']));

    $result = $con->query(" select * from users where email='$email' AND password='$password' ");

    $row = $result->fetch_array(MYSQLI_BOTH);

    session_start();

    $_SESSION['UserID'] = $row['id']; //thinking this is the problem
    header ('Location: home.php');
    }

And here is the home php

<?php require ("func/insert.php"); ?>
<?php
session_start(); 
    if (isset($_SESSION['UserID'])) {
}
else {
echo "This session is not working.";
}
?>

via Chebli Mohamed