Local CO-OP/Splitscreen games to play with my little brother on PC?

Magicka games

• https://store.steampowered.com/app/42910/Magicka/
• https://store.steampowered.com/app/238370/Magicka_2/

Here's a few previous discussions asking the same thing, maybe you can peruse them.

https://www.steamgifts.com/discussion/rI7J6/which-local-co-op-games-would-you-recommend
https://www.steamgifts.com/discussion/FHyGq/multiplayercoop-games-you-are-looking-for-pc
https://www.steamgifts.com/discussion/wWgnU/games-to-play-in-couple

Rubber Bandits, It Takes Two, Human Fall Flat, Stick Fight, just to name a few :)
https://store.steampowered.com/app/1206610/Rubber_Bandits/
https://store.steampowered.com/app/1426210/It_Takes_Two/
https://store.steampowered.com/app/477160/Human_Fall_Flat/
https://store.steampowered.com/app/674940/Stick_Fight_The_Game/

You can try BattleBlock Theater®. It's funny platformer and not hard.

If you liked previous game, you also can try Castle Crashers® from same developer. It's beat'em up. Up to 4 players could play it

https://store.steampowered.com/app/258970/Gauntlet_Slayer_Edition/
https://store.steampowered.com/app/1794680/Vampire_Survivors/
https://store.steampowered.com/app/710920/Darksiders_Genesis/
https://store.steampowered.com/app/413150/Stardew_Valley/
https://store.steampowered.com/app/1222700/A_Way_Out/
https://store.steampowered.com/bundle/12294/Trine_Ultimate_Collection/
https://store.steampowered.com/app/837470/Untitled_Goose_Game/
https://store.steampowered.com/app/1599660/Sackboy_A_Big_Adventure/

If he is only 6 I would recommend Boomerang Fu and Terror of Hemasaurus.

I played with my gilfriend in local co-op and we loved those games:
https://store.steampowered.com/app/453910/Love_is_Dead/
https://store.steampowered.com/app/710920/Darksiders_Genesis/ (maybe too dark for him)
https://store.steampowered.com/app/787810/Rogue_Heroes_Ruins_of_Tasos/ (totally loved it)

https://store.steampowered.com/app/1049320/River_City_Girls/
https://store.steampowered.com/app/423810/Marooners/
https://store.steampowered.com/app/442120/Pinball_FX3/

Kingdom Two Crowns was really nice. Rather easy, no fast paced action or button presses.

https://store.steampowered.com/app/850320/PHOGS/
Trine 3 & 4 (up to 4 players I believe)

Mortal Kombat and Resident Evil sure sound like good games for a six year old ^^'

Shadow Puppeteer: This one is mostly on the easier side and a short game.
Streets of Red: Street Brawler game, though on the harder side of games.
Wildfire: A lot of fun and chaotic at times. Maybe to complex.
Obscure: Plays similar to old Resident Evil games but in co-op. Probably also to difficult.
Party Hard 1 & 2: I think this works in co-op. Mostly some mindless murdering for .... reasons.
Disney Afternoon Collection: Only Chip n' Dale work in Coop. But that one is quite fun.
JumpJet Rex: Another platformer, movement can be challenging at times but has several checkpoints per map.
BroForce: Hilarious over the top action-game.
Phantom Breaker: More street brawling.
1001 Spikes: Trial-based platformer game with small but difficult maps.
Shovel Knight: Platformer game with medieval setting and mega-man like power-up system plus overworld map. From the trove only the first main campaign works in co-op.
Hammerwatch: Top-down dungeon crawling with lots of enemies and secrets. Though fast deaths can ruin your experience.
Crypt of the Necrodancer: Rhythm game with an unique gameplay. This is for sure to difficult for him. But it is a great experience if you reach the first skill treshold.

Brothers: A Tale of Two Sons
Highly recommended. A great adventure game that is not very difficult and with a great (albeit sad) story. I played with my son when he was ~8 years old and he cried at the end.

Portal Knights
Like Minecraft, but with a story and lots of different looking places to explore. Also much better graphics. Minecraft has tons of mods, servers and you can build insane stuff in creative mode, but as a vanilla game Portal Knights is a lot more fun in my opinion. It's not difficult at all and has split-screen. Another one I played through it with my son when he was ~8 years old and we had a lot of fun for almost 70 hours.

Lego Worlds
Another Minecraft like game. It becomes repetitive a bit faster than Portal Knights imo, but it is still fun to play and different from the other, story-driven Lego games.

Ithink the best option here is: https://store.steampowered.com/app/1361510/Teenage_Mutant_Ninja_Turtles_Shredders_Revenge/
Also nice option: https://store.steampowered.com/app/471550/Nine_Parchments/

You will have to do economics part here: https://store.steampowered.com/app/1356280/Kitaria_Fables/
You will have to calculate builds for you and brother: https://store.steampowered.com/app/1432050/Nobody_Saves_the_World/

Good option, if the toppic of the game is not too sad. Brother can play for big white cat: https://store.steampowered.com/app/972660/_Spiritfarer_Farewell/

Another variant to try:
https://store.steampowered.com/app/1049320/River_City_Girls/

The Yawhg

I am a sucker for local MP games, though more often than not I can't actually get my people to play them with me. XD

Wobbly Life would probably be enjoyable for you, I love it, and my brother liked it for a while, but hasn't played for a while.

Stick Fight is one of our favorites at our house, a fighting platform game with lots of funny moments.

Ultimate Chicken Horse is fun, might be a bit confusing, but difficulty can be customized pretty much to your liking, and is quite a bit of fun.

Vampire Survivors is one of my favorite games, and when they added local multiplayer I was sooo excited. It's pretty chaotic, and not exactly easy, but it might still be fun for him?

And Trine 4 and 5 should both be fun for you if you loved 1 and 2. I haven't played 3, but I think the completely different style made it much more confusing and difficult, but who knows? I also haven't played 5 yet, but I think they stuck with the stuff that worked for that again.

Oh, and all the Jackbox games are fun for all ages, they are always a blast at parties, though most aren't co-op, some are more team focused, and all support at least 6 players, using smart devices, computers, etc. as controllers. My neice and nephew both love them and they're younger than your brother.

You can play a lot of games that don't come with native splitscreen using Nucleus Co-op: https://nucleus-coop.github.io/

https://store.steampowered.com/app/564050/Bud_Spencer__Terence_Hill__Slaps_And_Beans/
https://store.steampowered.com/app/2142330/Bud_Spencer__Terence_Hill__Slaps_And_Beans_2/
:D

Disney Speedsstorm

Highly recommend Screencheat and Crawl, I think both are pretty fun and fairly simple games. I've played them with friends and we had a good time playing. ^^

Your brother is six and you already played all of that ? Just WOW .

Here are some recommendations:
Ticket to Ride (and any board game, why not)
Serious Sam 1 (both parts) HD Remastered
Racing: GRIP, Insane 2, Toybox Turbos
ANY Worms game, it's pure fun, especially the old ones
Brothers: A tale of two sons, but it'll just broke your hearth
Heroes 2-3, Disciples, Age of Wonders (maybe later)

Following this topic as I am looking to introduce my 4 years old daughter to gaming.

Distractie placuta !

https://store.steampowered.com/app/1286580/Ship_of_Fools/

Hey, I have played a bunch of co-op split games so I have a few to recommend you (I'm sorry if other people has already done it):

-Battleblock Theater is probably a mandatory recommendation. The more you progress, the harder it gets, but in the normal mode you respawn right away, so it shouldn't be too much of an issue,
-Following the same line, Castle Crashers is a pretty fun and simple beat 'em up, and I think specially for kids (some people might disagree).
-Similar to Castle Crashers, I recently had a lot of fun with Knights of Braveland, although it might be too similar to Castle Crashers, but in a roguelite version.
-Fling to the Finish is chaotic co-op fun, where you will laugh together with your partner because of the lack of cooperation or you will blame the other for holding you back, you decide. it is silly and a lot of fun (but some modes might be hard). It also has 2v2 mode if you want to challenge more people
-The Adventure Pals looks like a lot of fun, BUT I haven't played it, so I just recommend it based on what I have readed.
-Fueled Up is basically Overcoooked! but repairing ships. I think it is a really underrated game, but it might be too hard at some point. I would at least recommend you to take a look at it.
-Hotshot Racing is a simple and fun racing game, although the extra modes were a bit disappointing.
-Monaco is quite a popular game that can be played in local co-op, but it also could be a bit hard for your brother, because sometimes requires a lot of strategy an cooperation.
-Bread & Fred is fun and frustration. If you don't want something too hard, maybe you shouldn't try, but take a look at it, you might enjoy it anyways.
-The Trine saga is another mandatory local co-op experience. It has platforming, puzzles and combat, being puzzles sometimes a bit harder but nothing that will make your head explode (platforming and combat are fairly simple).
-Road Redemption is another great option, although it might be a bit violent if your brother is 6 years old... It's basically motorcycle racing, but your objective, besides winning, is to beat your enemies up using the weapons you find on your way. It can be played in co-op or pvp (no idea up to how many players).
-Pummel Party is a great party game, if your little brother is not too competitive.
-Invisigun Reloaded is another party game pretty similar to the classic Bomberman, but with shooting and superpowers. The game is quite unique and for me it is an underrated gem of party games (up to 4 players pvp).
-Porcunipine is another funny little party game.
-Redeemer is another top-down beat 'em up that looks pretty good, but I haven't tried it yet.
-Ship of Fools is quite a fun roguelite to play in co-op. It is not hard, specially in co-op.
I can recommend you a lot of roguelite that are a lot of fun in co-op... but they might be a bit hard for your brother: Nuclear Throne, Enter The Gungeon, Wizard of Legend, Voidigo and Blazing Beaks.

My little universe https://store.steampowered.com/app/2328750/My_Little_Universe/

You can even select that the avatar auto gathers stuff if you are near and facing resources, to make it less button heavy.

Pewdiepie game is great to play split
https://store.steampowered.com/app/390520/PewDiePie_Legend_of_the_Brofist/