One of the best online multiplayer shooters: Warface
Warface is a free-to-play first person shooter game by Crytek which lets you compete with people around the world, or play campaign missions with 5 player co-op. I have played this game for 2 years, and it's very good. Use your currency to buy new weapons and gear. Although Warface is a good game on it's own, there are some flaws to it. Online mode can be extremely difficult, as most players are very experienced. So I don't recommend this mode for beginners. Start off with campaign. It will be much easier in online mode with that practice. Like I said, it's free to play, so you don't have to use up your money and take the risk of wasting it on something you might not like. I would recomment this game for people who like shooters, because this is a pretty good choice. You are a soldier from the team Warface fighting with your rival, Blackwood. Blackwood runs experimants on people, starves countries like Australia, and it's up to Warface to stop them. There is a lot of action and suspense in this game, so that's a good thing.
Now we talk about age limit. The recommended age limit is 16 or older. However, if your child is mature enough for such content, I would say you let your child play it. The violence isn't that bad, there's barely any blood, I guess the swearing is a bit of a problem, but since you don't have to play campaign mode, swearing can be avoided. However, online mode can include players cussing each other out and cyberbullying. You can report such players, though. Which is a benefit. I would say that Warface should be rated 13 or older. This is all I have to say for age rating, but since this is bananatic, I gotta say some more.
So players can use different weapons to kill each other with, such as sniper rifles, ARs, CRs, SMGs etc. etc. However, there are weapons that are released sometimes, that aren't violent at all, such as water guns.
So, in conclusion, the content in this game isn't too bad for a thirteen-year-old to play. But if you want your child to play later, then that's fine.
So, the overall experience for Warface was great. However, I will admit that it can get boring pretty quickly. So I'd say after 1 or 2 years, you should look into other games for your kids, otherwise let your kid play, and let HIM look into other games. Again, this is bananatic, and I gotta say some more.
There are a few downsides for Warface too. Firstly, buying weapons is used by currency, called Kredits. Kredits cost real money, and I don't like the fact that people can only earn a few credits from matches or missions (a gun can be worth 2000 kredits, which is 20$). If you have money to burn, then buy it if you want weapons in Warface.
Also, the servers are pretty laggy, especially in PVP matches. Although lag is a problem, there is another downside. The pairing is TERRIBLE in online mode. For example, you're new to the game, and you join an online server, but you are supposed to fight a really good player, and it's pretty unfair. Crytek should improve the game a little bit, but other than the downsides, the gameplay is amazing.