While what Fightest says is true, I find it more linked towards adulthood.
As a child, humans know next to nothing. You can't grasp hard concepts, large words need to be defined by smaller words, reading is a big plus as well! Obviously, goals for children are lofty, since they mainly center around learning as much as they can.
This is essentially what Game freedom, or "exploration" potential is all about - the need to go out on your own and learn what you need to to survive or progress in the world.
The Sonic barrel is a good example of this for me - I was only a few years old when I got my first game console, the sega genesis, and my most favorite game on it was Sonic 3. Yes, that sonic barrel. It is considered a major roadblock in the game simply because it follows from a game design that it only ever essential or even helpful exactly once, is never explained, and does not follow from anything else logically. It's also almost impossible to get past it without figuring out the trick. I only remember having to restart this level ONCE in my entire childhood - I figured it out quickly. Give this game to an adult who tries to figure things out logically, they will never get past, yet as a child it only took me two rounds to figure it out completely and enjoy the rest of the game.
I had another example from Mischief Makers, but I don't have enough of an idea of what it was to employ it properly. The thing is, you'll find lots of this sort of thing the further back you go in gaming history. FFI Gives loose suggestions of where to go next, Many RPG games don't even give you directions and just dump you in a giant maze (Others still taught you to talk to as many strangers as possible just to figure out what's happening), and even Mario rewards sitting around and breaking every block you see with coins or warp points. It's easy to look back into the games you played as a child and wonder to yourself "God damn! how did I even beat this?"
The reason this goes away as we grow older in my theory is because by this age, learning has to be a much more refined process for us (or in some cases, we believe learning isn't important anymore) and our focus shifts more towards getting things done. Getting things done is progress, and it usually means we're contributing. This increased emphasis as it equates to game playing results in a loss of appeal, much as Fightest described.
In any case, I've written five paragraphs on the subject, so I'm out for now.