In my Catan review, I mentioned Catan: Junior's generous trading system. Since then I've played the game a few more times with my children and have a better feel for how it plays. Spoiler: it's fun and quick!
Catan is already fairly lean system, so the Junior version has limited options to simplify. The map and starting positions are fixed, which speeds up setup considerably. It also avoids the problem with the original where the all-important initial position draft so strongly influences the rest of the game. As far as I can tell, each color's starting position is different, but fair. In fact, everyone starts with access to each resource expect gold and is equally able to build toward the river islands where gold may be found.
Only one die is used which means each number has equal odds of being rolled. It's still possible to have a bad run of luck, but the range of outcomes is considerably compressed. In addition, 1:1 trade with the marketplace and 2:1 trades with the stockpile mean it's relatively easy to get the resources you need to build just about every turn.
The range of options of what you can do with those resources is similarly reduced. There are no city upgrades and buying cards won't give you secret victory points. Instead the goal is to build seven settlements and you get to place one settlement if you have bought the most development cards. So no longest road or biggest army bonus. Instead of requiring two road segments between settlements, only one is needed.
I should point out that the theme of Catan: Junior has been shifted from settlers to pirates. So the settlements are called pirate lairs, the connections between lairs are pirate ships and the robber who moves when someone rolls a six is the Ghost Captain. Development cards are named after the parrot mascot Coco. It's a more coherent and compelling theme than the original.
One risk of simplifying games for children is they become mere activities. Game likes Candy Land or Chutes and Ladders are races to the finish based entirely on chance. Catan: Junior isn't that. Players must plan their trades and decide what they will purchase each turn. When they move the Ghost Captain, they chose which resources they want and which island to make fallow. These decisions tilt the game's luck.
It's a quick game. We easily get 4-player matches done in half an hour including setup and put away time. What little downtime exists comes when another player is deciding on their purchase plans. Even if you didn't have resources to collect each time the die is rolled, you'd want to pay attention to what other people are taking from the market and where they are preparing to build.
I'd be tempted to say I'd play this game with adults, but I think it falls a bit short of other games in my collection. The choices aren't quite interesting enough. In particular, I think the optimal strategy is to go for Coco tiles. Since you'll need gold to buy them, you'll want to start by expanding into the river islands. (Begin with the the number you don't yet have.) Only build ships when you don't have a place to put your next lair. Consider taking gold off of the market even when you don't need it yourself. Use the Ghost Captain to target the player (other than yourself) who has the most lairs.
This strategy doesn't break the game by any means. But it does limit the impact of the decisions and increases the luck. Come to think of it, this may be the problem I have with the original Catan too. Despite having more choices, those decisions don't influence the results enough to be worth the complexity. Streamlining Catan: Junior has the considerable advantage of being a smoother and shorter experience.