We sometimes play a custom "Wingman Mode" with our 5 year old. I can't recommend this invention highly enough. My wife and I will hang back and do everything we can to run interference so our son can win. This includes ramming others off the road, diving in front of shells, or driving backwards with a Fire Flower and picking off competitors. You get better items because you're not in first, the kid still has to participate and try, and it's a novel way to play an old game.
I do something similar for my 5 yo, it actually makes for a more fun challenge than just stomping the 50cc AI. until he starts the smack talk, then he gets rekt
When I was young I used to get so unreasonably upset, crying that "the game cheats!" and my parents would make me turn off the console for the rest of the day until my attitude improved. They, and eventually I, just thought I was bad at handling failure.
Lo and behold, 20 years later, do some deep dive into the code and the way Mario Kart actually functions, turns out that mfer DOES cheat like hell, constantly. Like literally every second the game is running the CPU racers are cheating. They'll rubber band to your speed to make sure an opponent is always on your ass at all times, they straight up ignore walls and out-of-bounds slowdown, they roll good items they shouldn't be able to have in their position - MK is crooked as hell in all possible places that the devs could sneak cheats into.
I still have yet to receive an apology about this.