Well I'd say that the Orange Box is an amazing package of games that, although may be rather violent, are fun, with nothing that young teens these days wouldn't be able to handle. However, each game is totally different with different levels of badness.
Portal- Portal, despite being rated teen, doesn't really involve any violence. A bit of blood can be splattered on the wall if the player is shot, and an evil robot threatens to kill the player, but all done with a kind of quirky humour. The gameplay in Portal really makes you think and is very clever. I could even say it could be educational. So in conclusion, Portal would be appropriate for kids 10 and up.
Half Life 2- HL2 and it's episodes are all pretty gloomy and very violent. However, the storyline is intriguing and the game itself is a masterpiece. Since it is set in a bit of a post-apocalyptic time, corpses can be seen often throughout, and quite frightening species of aliens are often encountered, the most intense being the 'headcrabs', which jump on peoples heads and turn them into gory looking zombies. Despite the high amounts of violence, the unity of the surviving humans is something to be inspired by, and it is nice, near the end of the game, to liberate the city. All in all, HL2 is something for older kids, and is rather gory, but doesn't include anything that could affect people too much.
Team Fortress 2- TF2 is purely multiplayer, with the whole point to verse people in death matches over the internet. Although it is quite bloody, all the graphics are very stylized, being somewhat cartoony. I personally find this a very fun game, however is only appropriate in moderation (you don't want to be on a killing rampage for too long). However it is highly addictive (one of my friends has played 350 hours on it in the last few years, which I feel is too much). I'd say that TF2 doesn't really have many benefits, apart from being able to play with friends, and I'd say that TF2 shouldn't be played by small children due to it's very 'killy' nature.
Overall, the Orange Box is a truly amazing package, that is great value. However, shouldn't be played by kids under 14 years old, or otherwise already corrupted by high school. Again, it is rather violent but doesn't including anything that would be 'too much' for teens.
Thank you for reading.