With the release of Drupal 7.76 sort order for element children for renderable arrays is now consistent between php 5 and php 7.
If you are currently using a version of php 7.x you will not notice a difference after upgrading.
For those still using php 5.x, after upgrading to Drupal 7.76, you may notice a change in the sort order of element children.
Note: While PHP 5.3.x, 5.4.x, 5.5.x and 5.6.x are still supported for Drupal 7 please be aware that PHP 7.2.x is currently the minimum recommended version of PHP for Drupal 7.
Please check with the official recommended versions of php for Drupal 7 by clicking this link.
The element_children() function is called in many places in core (and contrib):
https://api.drupal.org/api/drupal/includes%21common.inc/function/element...
A couple of examples of usages which may be affected by the change in sort order for PHP 5:
https://api.drupal.org/api/drupal/includes%21form.inc/function/theme_tab...
https://api.drupal.org/api/drupal/modules%21system%21system.module/funct...
