Unclickable menu items is not recommended because it leads to issues like this and it makes browsing your site more difficult. You also miss out on an important opportunity to show the relationship between those sub-pages using a "disambiguation" page which will help with SEO.
We always suggest having any page you would like to set to "unclickable" be a landing page with each of the sub-pages listed out with descriptions. See these pages for examples:
In the very least, I suggest adding the Child Page Site Map to the page so when people manage to get to the page, they will be able to see what pages exist under it.
I hope this helps.