This is an amazing game. Very intelligent, very thoughtful. Its a video game, that requires THINKING!!! Can you believe it??? Thinking, on a TV screen! Sell that headline to the media. Even after you finish the single player, you still have the co-op that your kid can play with you. Its so simple, there are only 3 buttons required - left trigger, right trigger, and the jump button. The two triggers are confusing at first, but the game starts easy so you can learn the game mechanics as you go, even as a person who has never played a video game before.
The only thing I noticed, was the issue of maturity. The game is very funny, and anyone who doesn't think Wheatly (played by Stephen Merchant of The Office) is hillarious, either is very hostile, or has no sense of humor. He makes jokes about you having brain damage, and a computer not recognizing a cockney accent (if you remember that Siri bug from 2011), which is all very funny to a person who understands the jokes.
This lack of maturity/brain-development that hates humor can also lead into frustration when solving puzzles. At times, the puzzles require thinking "outside the box", sometimes quite literally. This may be an excellent problem solving lesson for your child if, if he/she is independent and doesn't seek a walk-through every time they have a problem. Otherwise, it will be a lot of time of you playing and them watching, rather than them learning the excitement of figuring something out.
Another thing to watch for is the violence. The player is not being violent themselves, but is rather using wits (and portals) to take down the turrets and avoid toxic gasses. The main antagonist, GLaDOS, will attempt to murder you (as revenge from Portal), as well as be a generally horrible, moral-less robot. (In the end, she softens and switches sides to let you leave Aperture Labs. (: Happy ending.)
As I said before, this is an amazing game with extremely difficult puzzles. The reason for my age rating is due to the difficulty of the puzzles - not the violence. Kids below a certain learning curve will become somewhat frustrated, but persistent, and then excited. I think that the average cartoon is more violent, and less rewarding than this game, so if any parent has beef with video games in general, saying that they make kids "Stupid" and "Violent" - this is my counter. Let generation Z teach you a lesson in Rock and Roll.
The game has a Parkour-esque movement scheme. In simple, you're moving from point A to point B using only your surroundings and your wits. The Portal Gun serves as your body and strength, your high fall boots replace kinesthetic awareness, and your mind serves as your discipline and your, well, mind.