This site is being deprecated.
Please see the official X‑Plane Support page for help.
I am not from Laminar Research; just a flight simmer from downunder.
My understanding of your question is that there are a number of people using your Mac and each person has their own login. Irrespective of who has "logged in" (your problem) X-Plane can then be started. There is no checking by X-Plane to ascertain if the individual wanting to use X-Plane is authorised to run the software. The short answer is "YES".
However there is a system that can be setup within X-Plane whereby you, the official user (parent) can setup a password that prevents others (your children) from making changes to your system without your approval/supervision/knowledge. Memory tells me it is called "Kiosk" mode. If you decide to use this method you need to ensure your "kiosk" password is stored/secured/recorded in a safe area and you remember where, in the event you are asked for it or you want to change your system configuration at any time. Many have failed to do this and contact Laminar Research, with "Cap in Hand" asking for help in trying to recover their locked out system.
Read the manual found at https://www.x-plane.com/manuals/desktop/
What can also happen is you are able to install X-Plane on any number of computers but can only run one version/copy at any one time. With a digital download version you have to be connected to the internet at all times. Why? The digital download performs a silent background verification check with Laminar Research advising the software is being used using the allocated product key. If two versions are being used at the same time with the same product key the software determines that one copy is a pirate version and your system shuts down. Permanently? I don't know because I haven't tested what happens.
This site is no longer being actively maintained.