Use array_diff_assoc() or get difference of multidimensional arrays

To check multi-deminsions try something like this:

$pageWithNoChildren = array_map('unserialize',
    array_diff(array_map('serialize', $pageids), array_map('serialize', $parentpage)));

• array_map() runs each sub-array of the main arrays through serialize() which converts each sub-array into a string representation of that sub-array
  • the main arrays now have values that are not arrays but string representations of the sub-arrays
• array_diff() now has a one-dimensional array for each of the arrays to compare
• after the difference is returned array_map() runs the array result (differences) through unserialize() to turn the string representations back into sub-arrays

Q.E.D.

Very nice solution from @AbraCadaver, but like I've stated in the comments, there might be cases when the elements of associative arrays are not in the same order everywhere, thus a custom function which will sort them by index / key first is handy:

function sortAndSerialize($arr){
    ksort($arr);
    return serialize($arr);
}

array_map('unserialize', array_diff(array_map('sortAndSerialize', $pageids), array_map('sortAndSerialize', $parentpage)));

Right way https://github.com/yapro/helpers/blob/master/src/ArrayHelper.php

class ArrayHelper
{
    /**
     * @param array $array1
     * @param array $array2
     * @return array
     */
    function arrayDiffAssocMultidimensional(array $array1, array $array2): array
    {
        $difference = [];
        foreach ($array1 as $key => $value) {
            if (is_array($value)) {
                if (!array_key_exists($key, $array2)) {
                    $difference[$key] = $value;
                } elseif (!is_array($array2[$key])) {
                    $difference[$key] = $value;
                } else {
                    $multidimensionalDiff = $this->arrayDiffAssocMultidimensional($value, $array2[$key]);
                    if (count($multidimensionalDiff) > 0) {
                        $difference[$key] = $multidimensionalDiff;
                    }
                }
            } else {
                if (!array_key_exists($key, $array2) || $array2[$key] !== $value) {
                    $difference[$key] = $value;
                }
            }
        }
        return $difference;
    }
}