The easiest game in the world to play is probably chutes and ladders. There isn't any strategy. You can't be "really good" at this game. Hours of practice aren't going to make you dramatically better than you were before. The game is incredibly simple because the rules are this:
You spin a spinner, which moves you forward a random number of spaces. Sometimes you get lucky and get to move forward even more spaces. Sometimes you get unlucky and have to move back a number of spaces. Repeat until someone wins.
The only thing you have any semblance of control over is the spinner. And you don't even control that. If you try and flick it the barest amount to get it to move a mere centimeter onto a "good" number people will say that doesn't count and make you flick the little plastic pointer as hard as you can. It's random. It's like spinning that big wheel on The Price is Right, only with even less thought involved. You have no say in what happens, you just have to be present at the appointed time to spin the spinner; to try and get lucky.
The one good thing is that it's easy to beat your parents at this game. In virtually every other contest they're going to defeat you handily, but in the land of chutes and ladders the playing field is level. Hi Ho Cherry O operates on a similar principle, except you have to be able to count to ten. Forgetting how much "ten" is, is the only thing you can get wrong.
But there is an even easier game: Candy Land. The rules are very similar.
You draw a card, which moves you forward a random number of
spaces. Sometimes you get lucky and get to move forward even more
spaces. Sometimes you get unlucky and have to move back a number of
spaces. Sometimes you have to stay where you are until you draw the "right" card. Repeat until someone wins.
The only thing you have any control over is... nothing. You draw a card when it is your turn, and drawing cards is something its hard to be "good at" beyond having fine motor skills.
Candy Land and Chutes and Ladders aren't really games as much as they are lessons about how to play games. You're teaching concepts about the basics of gameplay, like how "taking turns" works. It's the most fun way to teach a child about waiting. It's about how abstract concepts like player controlled pieces, movement randomizers, win conditions, and bonuses/penalties work. These are the building blocks for more complex games. Expecting your 3 year old to 'get' Settlers of Catan is just ridiculous.
But I think beyond this, there's a separate lesson that comes up: the lesson that this universe is one where there are lots of things out of your control, and that really wanting something doesn't mean it's going to happen. In Candy Land, there's nothing you can do that would change what card you draw because you have to take whatever card is next.
Once the deck is shuffled, the game is set. You're basically sitting
around waiting to see what fate has decided. Chutes and Ladders is only
marginally better because the "winner" isn't pre-determined as soon as
the pieces are set up; it's more like waiting around to see what
The broader lesson is how to be gracious in defeat. The first time you lose, you get mad, you throw things because it's SO UNFAIR that you lost, and so you are sent to your room. It doesn't take long to learn that that attitude ain't gonna fly. In the land of candy, there's nothing you could have done to emerge victorious. Everyone has the exact same amount of say in who will win, which is no say at all. It's perfectly fair because it's entirely unfair: the winner is going to be whomever the cards say it will be. Even if you deserve it more, even if you've lost every game and your brother has won every game and you feel miserable, if the cards say he wins this game too then tough luck kid.
These games are such a low-stakes way to get into the realm of metaphysical injustice at an early age. Hey kids! Let's learn about disappointment! doesn't quite have the same ring to it as Hey! Let's play Candy Land!