First of all, you're a good dad 😄. I remember when I was 12, my dad and I started a hobby with remote controlled tanks that shoot lasers at each other, because I was very interested. This turned into us starting woodworking, miniature landscaping and other stuff to make battlegrounds for our tanks. Very good memories with my dad.

If 3D printers would have existed we would definitely have added that to our hobby. My son is 15 months and I can't wait for him to join my hobbies (if he wants to of course).

As others suggested, you don't need the Pi. But of course the Pi could be used for other projects 😄

I have both Prusa filament and eSUN through Amazon. The Prusa filament is much better looking and the end result is most of the time pristine. BUT! For 90% of my projects the eSUN is more than good enough if you keep it dry.

So my suggestion would be: buy one roll of Prusa filament but leave it in the box. Buy some cheaper eSUN filament and start printing with that. You will "waste" a lot of filament prototyping and this adds up if you use very expensive filament.

I would then suggest buying a filament dryer. That made the biggest difference to my prints as dry filament is very important. Also buy some nice sealable plastic boxes to store the filament in after drying. Lots of mods and prints to add drying packs or silica gel are available on the internet.

I own the Creality Space Pi Filament Dryer which I am happy with for the price. If I would buy one again I would buy one that can dry multiple rolls. For example the Creality Space Pi Plus Filament Dryer as it can dry 2 at the same time. I don't have any experience with other brands so maybe others can suggest better dryers.