Child item does not show up under assigned parent in drop down menu

The children I create do not show up under their respective parents for me on the front page nor any other than the primary link pages they belong to.

I set up the primary links menu as instructed which works just fine. However, when I create a child page and assign it to a parent from the primary links list, it doesn't appear in the drop down menu on the front page nor any other (sub) page, BUT it does appear on the parent page it is assigned to:

Home page:
About
Services >> Child page in question does not appear in drop down menu
Contact

About/Contact pages:
About
Services >> Child page in question does not appear in drop down menu
Contact

Services page:
About
Services >> Child page in question DOES appear in drop down menu
Contact

I might be missing something here, but I checked all my menu settings (the primary links show the full list as well as the child item in correct order; all of them enabled) and double checked that all is well and toggled on in Themes and Blocks and am not sure where else to look. Any advice is very much appreciated.