RetroGaming

Magical Quest 2 & 3 are very good for that. They already know the characters, and the games are beautiful and pretty good gameplay-wise.

You play together and if the child loses all his/her lives, he/she can steal yours. For difficult sections or bosses, you can do it alone.

There are new costumes regularly so the child wants to continue to discover the next costume, and its associated powers.

Magical Quest 2 is easier than 3, so I think it’s better to start with this one. You can either play as Mickey or Minnie.

In Magical Quest 3, you can either play as Mickey or Donald. Donald is meant to be played by the child because his gameplay is a bit different (with his soldier costume which is wooden barrel, preventing him to sink while Mickey has a silver armor which kills him if he goes into water with it). It’s not that difficult to play as Mickey (my nephew did not want to play as Donald and we had no major issues).

Mortal Kombat is pretty tame I hear.

( ͡° ͜ʖ ͡°)

Super Mario by far IMO, basically all of the games.

5yo is probably still too young to understand Zelda.

A c64 emulator? Then basically anything, LOCO maybe?

Turtles in time

World of Illusion (Genesis)

Oh, and sorry for so many responses, but I figure that posting these separately will let the votes give you some idea where to start.

The votes I've seen so far very much reflect the order I would try these games out with a five year old gamer.

Kirby Super Star

A GREAT game to play with kids is called "Stacking". Looks like there's a Linux version so you might be able to get it running on the Pi:

https://en.m.wikipedia.org/wiki/Stacking_(video_game)

PlayStation 3, Xbox 360, Windows, OS X, Linux

The gag is this...

You play the smallest of a set of Russian nesting dolls and you want to re-unite with your family.

In order to do that you have to solve a bunch of puzzles in a world filled with other Russian nesting dolls.

You can jump into any doll one size larger than you, and you can jump out to be one size smaller.

Each doll has a specific skill or ability, so by swapping bodies, you use the various skills to solve the puzzles.

The challenge is, you might find one that has the right skill, but you're too small to jump into them, so you have to find the right chain of dolls to size up and size down to do what you need to do.

Trailer:

https://youtu.be/oEJtypcyL5I

City Connection, Bugs Bunny's Crazy Castle. While neither are co-op my mom and took turns playing crazy castle on the nes when I was a kid and we beat it. Core memory right there.

I think Tetris or Doctor Mario had 2 player modes but I'm not sure.

Does Sonic Spinball on the Genesis have multiplayer?

My kid used to love one of the Kirby games for the Wii, where the three of us could play at the same time. I can't remember the name of it, but I'm pretty sure it was previously released for the SNES. It was the one with Armor Knight, if I'm remembering the character name correctly.

Fun-N-Games (Genesis/Megadrive) is mostly single player, but has many mini games accessibile to young gamers.

It's single player, but too good to miss: "Richard Scary's Busy Town" (Genesis) is a fantastic open ended set of mini-games that are fun and accessibible to almost all skill levels of gamer.

Mega Bomberman (Megadrive) and Super Mega Bomberman (SNES) both have multiplayer mode where players can team up against bots, and the bots have adjustable difficulty (different bot skins have different AI).

Edit: Re violence - you blow each other and bot players up with bombs. Players that die disovle the way Pac-Man does.

My Famiclone childhood:

Mario Bros (the first one, with POW block in the middle.) https://en.wikipedia.org/wiki/Mario_Bros.

Battle City, known more by its pirated version name: Tank 1990 https://en.wikipedia.org/wiki/Battle_City

Are you committed to using the R.Pi1? You could emulate on your computer or phone (connected to the TV) to have way more options.

How adept is your little one with games? My 4 year old loves any and all Mario games. He plays sitting on my lap. I celebrate his successes and he passes me the controller when he gets to a section too difficult for him. This is mostly with Mario 3D land (3DS) these days.

Ms. Pac-Man (Genesis) is fully co-op throughout, and has adjustable difficulty by choosing smaller maps.

Dashin' Desperados (Genesis/Mega Drive) is a racing platformer, where the adult can control the difficultly by slowing down or backtracking.

Edit: Cartoon violence - you can freeze each-other, light each-others shoes on fire, and stuff like that. And everyone recovers in cartoon timing, of course.

Super Baseball Simulator (SNES) is competitive, but can be really chill if the adult player throws easy pitches, and the super powers are hilarious.

Super Dodge Ball!

Wai Wai World 2 on Famicom emulator. Don't need to know any Japanese to play and it has great cartoony sprites.

Bubble Bobble (NES) is great two player, though you're competing

Buster Bros (PsOne, and probably others) probably one of my top 5 co-op games of all time

Micro Mages (retro despite being released in 2019 because it plays on original NES hardware) probably top co-op of all time for me

There's quite a bit more but have various degrees of violence so won't recommend those (Contra, Heavy Barrel, Silk Worm, Jackal, Life Force, etc)

You know what? Gyromite and Stack-Up, the games made to be played with R.O.B. You play the robot. I don't know many co-op multiplayer games on the NES. Maybe Chip & Dale, or Mario Bros. (not Super, the arcade game - though in 2025, I suggest Kaetekitta(sp?) Mario Bros., the rerelease). Bomberman might have cartoon violence, but I don't think it's going to scar a kid.

On SNES, there's Secret of Mana if you want to try for depth. I forget if any of the sports games let you go co-op. Pocky & Rocky (and other cute 'em ups) might be fun too.

Actually, general suggestion, cute 'em ups. Cotton, Twinbee, Fantasy Zone, Air Zonk, and many of the Parodius incarnations (obviously Sexy Parodius notwithstanding).