Tears of Kingdom, GT7, Gradius V..

Hard to say since I grew out / bored of most of the series I used to like back then. I liked the simplicity, grid controls, manageable nr of units. Showing the latest civilization or sim city would be a deterrent lol. While showing GT7 in VR would leave me disinterested in settling for Grand Prix Circuit.

Also what do you define as show? Take a look or here's the game enjoy it fully. Showing modern games to untrained eyes is just very confusing. It takes a while to pick up on the controls and game language. You're showing someone used to a d-pad plus jump/fire button and games designed with minimal background (non gaming) elements, games that use 14 distinct buttons, 2 analog triggers, 2 analog sticks and still need radial wheels and other mechanisms to put even more functions on the controller. VR would be more intuitive to show but 'showing' the highly exciting stuff mostly leads to initial nausea and you have the same problem, not knowing the buttons. 

I would show Synthriders in VR for all those reasons. It's amazing to play, simple controls, you're static little risk of nausea and the experience levels are as good as Rez Area X in VR. (but without the disorientation) Heck video games hardly had sound effects when I grew up.

If you could sit down with your child self and teach him to play it would be TotK for sure. Get my younger self to play that before BotW, entire map still unknown! Just casually drop a Switch 2 off with TotK remastered :)

It would probably be a game that's visually stunning. So right now it'd probably be GTA 6?

Just seeing the difference of character and background designs, and gameplay from today's game compared to like the original Mario on NES would have blown my mind. Let alone, the change from 2D to just open world realistic 3D would have been enough too.

Probably nothing. I am afraid it would make me dissatisfied with what was then current gen and rob me of at least some of the joy I had. I started out on the Atari 2600 so I have gotten to be wowed by many generational leaps. If I knew for sure what was to come I would have instead been let down by those generational leaps instead of wowed. "nope, it isn't here yet". #oldpeopleproblems

Personally I think I would go with BOTW; it's not the most visually advanced "modern" game (though it still would have blown my mind as a kid used to N64 graphics) but the systemic nature of it where so much of it is dynamic and interactive was how I used to imagine games of "the future" would be like back then, so that would have really captured my imagination.

Breath of the Wild for me.
It’s what I dreamed 3D Zelda would be before we ever had a 3D Zelda.

Some others that my mind ran by were any Paradox Grand Strategy game or 4X (probably Victoria, CK, or Stellaris), Witcher 3, Xenoblade Chronicles X, Animal Crossing New Horizons, or No Man’s Sky.

None. That would be a nightmare. Only I know what future games will look like? I would probably be a prick about it and people would dislike me for it. No thanks.

Depends how old my child self is. I would likely show them whatever I was interested in at the time. Pokemon and Digimon were a large part of my childhood. I hear that modern Pokemon games aren't great, so perhaps we can go with a Digimon game.