If you make the link simply a hashtag (#) that will do the job.
However, keep in mind that some mobile devices (particularly larger tablets) can have a difficult time getting dropdown menus to work properly. You’re typically better off to create a simple landing page for those, or even just have them link directly to the most important child page below them.
Another way that I use sometimes is that I use the Yoast SEO plugin, and that lets me set a redirection URL on pages, so for the landing pages that I don’t want anyone to see, I can set that page to redirect to the “correct” URL that I want users to see.