If your prime concern is not to inconvenience other users, perhaps adopt a habit of logging out of your own account rather than leaving it to suspend and lock. In this way you only need to switch user, do your thing, logout, and switch back to the kid’s session.
I feel that might workaround the issue without much fuss. 
Musing:
There are frequent issues concerning black screens (mainly, they seem to be Nvidia related); Search: black screen.
It’s possible that the black screen you observe isn’t strictly a consequence of user switching, and may be related to one of many other issues.
If you happen to experience other black screens in different circumstances, even occasionally, it might be worth searching though those search results to see if any might be applicable to your environment.
Otherwise 
Then, that certainly opens an avenue of research.
I haven’t used an Nvidia (anything) for at least a decade, and my graphics issues have been few and far between (using AMD graphics). Most graphic issues I see seem to be Nvidia; that said, there are always exceptions; some claim to be equally as troublefree.
I would suggest not dismissing the reminder given by @nikgnomic previously about the BIOS update. Updating a BIOS can often solve issues you might not even be aware of.
UEFI BIOS v1.18.1
was released on 2024-11-12 and is marked as critical.