Recommendations for father and 10 years old son to make them love gaming?

Stardew Valley.

Its a calming farming game. Multiplayer came out two months ago, and the game is good for everyone from casual to "expert" gamers.
It's also great for bonding.

Minecraft might be a good one

Buy him classics of every general genre: shooter, horror, puzzle , driving... Then he will know what types of games he likes, for example my father love driving games like formula one ones(lol) and I love fps.

Any way, I think its too soon for gaming, what a pity.

The Swords of Ditto
Don't Starve Together
Magicka
Lovers in a Dangerous Spacetime
BattleBlock Theater

LEGO games

Not on Steam, but Zoo Tycoon is a nice game for me back then. Perhaps you might want Zoo Tycoon 2 instead for the better graphic.

For non-gamers they usually get frustrated by losing, especially any games that require quick reactions, they get confused because they are not used to the controls or using mouse/keyboard or whatever.

So I'd suggest casual games, or also any game with open world that lets you just roam freely and mess around without being limited strictly to the story/missions.

in 1996 i was 10 years old:D and i played RESIDENT EVIL !:D
what about racing games, btw.

I'm a father myself, son is 9 years old - and he loves LEGO. With those you cannot miss - every movie etc has a proper game. Also some racing and shooting (Sonic and All-stars Racing Transformed and Toybox Turbos), creative like Minecraft, platformers like Rayman Origins, Castle of Illusions, Jumpjet Rex, a little bit of strategy in HoMM V and VI (he didn't liked the graphics of III).
I've started with Quake II, Carmageddon, Fallout and Earth Siege II - but those were times, when the graphics were just suggestive, not showing everything :P

Cat Quest is good. Portal Knights too. My 9-year-old son really likes them both.

Minecraft, Roblox, and Fortnite are very popular among kids. I would not recommend Roblox, but the other two are pretty good.

Terraria, all the LEGO games, Sea of Thieves etc.

Are you looking for games they can play together on the same PC or just games for them to play in general?

These are some good local coop games I've enjoyed with my niece:
Adventures of Shuggy
Broforce
Duck Game
Gang Beasts
ibb & obb
Keep Talking and Nobody Explodes
Lovers in a Dangerous Spacetime
Monaco
Move or Die
Nidhogg
Overcooked
Rocket League
ROCKETSROCKETSROCKETS
Skullgirls
Trine
Trine 2
Trine 3
Worms (all of them)

To suggest games in general, it depends on what they're interested in.

As mentioned already, the Lego-Games are great! There are so many, so I'm sure whatever his son likes best (Pirates, Dinosaurs, Ninjas, Magic, Star Wars, Batman), you'll find something for him. There is so much to discover and they are child-friendly.
Yooka-Laylee is also a great game and shouldn't be too hard.
Oh, and Louie Cooks is a game a 10 year old child might love ^^
https://store.steampowered.com/app/398480/Louie_Cooks/

Well good luck on educating them on scammers, phishing, e-mail spam, viruses and generally operating the OS. I assume you'll be the tech support for the next few years? :D

The 10 year old is going to have no problems figuring out what he wants to play. Let him choose. And once in a while maybe surprise him with something you think is cool.

The dad who has never gamed... don't worry about it. He doesn't need to be convinced.

I haven't tried it yet myself yet since it's local multiplayer only, but Overcooked looks like a great cooperative party game for 2-4 players

These are the games my 8yo and I have enjoyed together in co-op:
ibb & obb
Lovers in a dangerous space time
Never Alone
Lego Games (We've played Batman and the Star Wars Complete)
Super Blood Hockey

and the games we've played together:
Midtown Madnes 2
Escape Goat 1 & 2
MX vs. ATV Reflex
Burnout Paradise
Adventures of Shuggy
Crash Drive 2
Goat Simulator

and we've dabbled a bit with Baldur's Gate. My kid really wants to like it, but there's just a bit too much reading for him.

Never alone :D

I understand that the hardware question is already settled, but there certainly isn't any better choice than Nintendo to get people into gaming. Be it young or old.

Rocket League. It's easy to learn but hard to master.
Or any LEGO game. There are so many out there.

Mini ninjas, Stories the path of destinies, I play these 2 with my girlfriends sister, she is 9, and she really enjoys it.

Definitely Lego games as many have mentioned. Marvel, Star Wars, DC etc. etc. Lego Worlds is actually pretty awesome as well.

Pinball FX3 (the Sorceror's Lair table is free and you can buy DLC table packs)
The Disney Infinity Gold collection
Castle Crashers
Sonic Mania
Portal Knights

Oh if they like baseball I hear that Super Mega Baseball: Extra Innings is pretty fun.

Already said but I recommend Lego games. I play with my 5 years son and my 10 years daughter without problems.. They saw the movies and like the related lego games.