Install the plugin Post Types Order
Solution is use:
function objectRSort(&$object, $key)
{
for ($i = count($object) - 1; $i >= 0; $i--)
{
$swapped = false;
for ($j = 0; $j < $i; $j++)
{
if(is_numeric($object[$j]->$key))
{
if ($object[$j]->$key > $object[$j + 1]->$key)
{
$tmp = $object[$j];
$object[$j] = $object[$j + 1];
$object[$j + 1] = $tmp;
$swapped = true;
}
}
else
{
if (strtolower($object[$j]->$key) > strtolower($object[$j + 1]->$key))
{
$tmp = $object[$j];
$object[$j] = $object[$j + 1];
$object[$j + 1] = $tmp;
$swapped = true;
}
}
}
if (!$swapped) return;
}
}
And just include this code:
$child_pages = get_field('child_pages');
objectRSort($child_pages, 'menu_order');