How can I use in_array if the needle is an array?

Use array_diff():

$arr1 = array(1,2,3);
$arr2 = array(1,2,3,4,5,6,7);
$arr3 = array_diff($arr1, $arr2);
if (count($arr3) == 0) {
  // all of $arr1 is in $arr2
}