Hi. I’ve been thinking about trying out Linux for a while now (haven’t used it before).
Welcome :)
I have 1 PC which I share with my son. I mainly use it to browse the web, listen to music, watch movies and TV shows, Office for work, etc.
Depending your 'MS Office ' expectations, you should have no issue using LibreOffice. 100% compatibility doesn't exist, though, but for most users it should work more than fine. For the most part, it is only a few advanced features and tools that are lacking, and some layout stuff. I write books under Linux as easily as I wrote them under, well, not a Windows PC in my case: it's a Mac.
I am not a gamer. So, for that I can't help much, but you have the ability to dual boot your PC and chose between Windows and Linux when it starts. Maybe that would let you use Linux while keeping a small Windows partition for your son games?
Here is one guide among many others (I have not used it myself, it's just an example there are plenty more): https://opensource.com/article/18/5/dual-boot-linux
FYI, you can try Linux directly from a live CD (or a USB stick) without even have to install it on the computer. It's really cool.
As for the distro I was considering Ubuntu.
You can use whatever distro you fancy, you can easily try a few different ones either by using the live CD/USB I mentioned, or by running them in a virtual machine — something I have never done myself as it's a bit too intimidating and techy to old-and-not-much-of-a-geek me :p
I use Debian (on my desktop) and Mint (on my laptop). Ubuntu is based on Debian, and Mint is based on... Ubuntu (from which it has removed stuff I'm not happy with in Ubuntu and added a few others I like). There is no good and bad distro, only those that you like and those that you... like less ;)
Edit: to a beginner, probably more than Ubuntu I would suggest Mint, at least if I can judge on my own personal experience: everything worked out of the box, including my stubborn Apple Airpods.
The rule is that apps are only updated for security reasons. Not because of new features.
So, new versions of apps may (or may not) be added to the next version of Debian.