I've played this game for over six years. As an adult with considerable discernment, I've made several long-distance friends, some of whom are international. It's this aspect of the game that keeps me playing as I've made several long-term friends there.
But as a parent I would strongly caution other parents to consider their children carefully before allowing them to play. Yes, there are language filters in the game, but most of the older children playing this game know how to sidestep them. I do not allow my own children to play before the age of 13, and then when and if they do play, they are in my guild (a shared group of friends in addition to your own "buddies") so I can keep an eye on them. As mentioned by another reviewer, characters can get married (something I do not allow my children to do) in game when a "wedding" is purchased with actual cash. My husband made a character so our characters could marry in game as I didn't want to be even virtually married to anyone but him.
The spending aspect everyone is warning you about is really not a problem if you understand a few things. First, a child (or anyone else) playing this game cannot spend actual cash by accident. You don't have to worry that a child exploring the content of the game could possibly rack up a huge bill to surprise you. Before NX cash (what they call their online currency which represents actual cash) is spent, it must be loaded onto the account. This is accomplished on the website, either through the purchase in a physical store near you of their Karma Koin cards, or through a credit card transaction. Beware if your child has stolen your credit card in the past, as this would allow them to load their account.
Outside of that, it's very easy to play this game while spending absolutely no actual cash at all. Characters can purchase clothing (armor, weapons, accessories) using the in game virtual currency (mesos) that are earned by killing cartoon monsters of various types. The monsters drop mesos, equipment items, and "etc." drops which are either used in quests or can be sold back to the Non Played Characters (NPC's) for more mesos. All of this equipment is sufficient for playing the game. A few of the "cash shop" (the in-game store where actual money is spent) items are very useful while playing, but are not required. Use this as a good opportunity to teach your children about wise spending. Buying $10 of nx a few times a year would not be a problem for most families and would provide the added lesson that buying an entire "for looks only" outfit from the cash shop (cash shop outfits are worn "on top of" your in-game armor for looks only....they do not provide your character with any benefits outside of a fashion statement) which lasts 90 days is a waste of money. At times there are permanent clothing items offered in the cash shop for a limited time, but there are more expensive in the short run (2 or 3 times more expensive but they don't expire). Other things like a pet, which offers functionality while playing the game, can also be bought as a permanent item during special cash shop sales.
If, like me, your budget is far too tight to allow even $10 or $20 in nx purchases a year, you can earn nx in game through the Maple Trading System shop. You collect items in game with your character as you complete quests and then you can sell them there to other players like a virtual flea market. Nexon (the maker of MapleStory) takes some of the nx involved in the transaction as a form of "tax", the seller gets to keep the rest. Each posting of an item (or bundle of one item if it's an etc. drop) costs 5,000 mesos to post. This method of earning "cash" for the items you want is not going to be fast or easy. But isn't that the lesson you want your kids to learn about money anyway? A lot of effort and considerable savvy and patience will have to be employed to earn nx for a permanent pet and it's accompanying permanent equipment and item slot expansions (the most useful cash shop items in my opinion, and ones that are permanent and do not expire in 30 or 90 days). I utilize this approach myself, so it can be done.
Outside of the language issues and the conversation that needs to take place about the cash that can be spent (each family should decide what's appropriate to be spent and stick to it), there can be some very educational aspects to this game. It certainly could educate about a virtual (and by extension a real) economy with not much work. I've often thought that economics professors should take a good look at this game for educating students about all the aspects of supply and demand. It takes work to gather items, and there's a chance in the process of gathering items considered valuable in game. The prices between players (both in the nx sales which occur in the Maple Trade System shop, and in the mesos sales which occur in the "free market" where players sell items to one another for mesos currency) fluctuate based on supply and demand. An item that's easy to get, no matter how useful it is, is going to have a low price. Items that are extremely useful and rare will have a high price. And there's competition between players to sell the same item, which affects how much can successfully be charged by the seller. There's also the benefit of learning to shop around, which takes time and some skill, and the disadvantage of being impatient as you search for an item you want to buy. All of these lessons are valuable in real life, not just the game.
There's also the teamwork necessary for the harder quests and more advanced (higher level character required) party quests. There's an entire code of ettiquette in game as to what's acceptable and what's not. I would strongly encourage any parent to PLAY a game before turning your child loose in it. I got started with online gaming because I refused to allow my children (the oldest was 11 at the time) to play a game (Disney's Toontown) before I'd checked it out first. I really wish more parents would do this. First, it gave me the benefit of learning what behavior would be rude, what would be helpful or polite, and what my child was likely to encounter while playing. In teaching your children to be polite in a store, you don't try to do that without ever entering a store yourself, right? The same holds true online. How your children treat people online DOES matter. There are real people on the other end of that internet connection that are being helped or hurt by your child's actions and either politeness or rudeness. I've encountered appalling behavior by supposed pre-teens and teens that I wish their parents could be made aware of. I truly believe if more parents played these games, either alone or alongside their children, the general demeanor in game would change drastically.
Although your child would certainly have no trouble spending several hours at a sitting playing this game (of course it's addicting or the company would not make money from players who continue to play!.. ever seen a restaurant serving horrible food remain in business?), you are the parent. Establish guidelines for your child's play. How many hours will you allow play? Should they have homework and chores completed before they may play? May they only play on weekends, or are weekdays acceptable if schoolwork is complete. Perhaps they need to "earn" time for play by doing certain chores? You're the parent! Don't allow whining and "but they want to" to be the deciding factor in what they are allowed to do. It's your job to protect them. If any game is having an adverse affect on your child, then eliminate it. It shouldn't matter how much they might complain or yell or be angry with you. Only you can decide what's appropriate for THAT child.
Make sure you teach them about online safety before allowing your child to play any online game with any form of chat. Do not trust chat filters to completely protect your child. Children should never give out information like their location (beyond country and state) to anyone online. Online friends are "strangers" and kids need to be taught that. No phone numbers, schools, streets, cities should ever be discussed, and if someone online asks for that information your child should immediately tell you about it so you can take appropriate action. It might be an innocent question from another young online gamer, but don't expect your child under 12 to figure that out for themself. Sharing what state/country you are in is fine in my opinion...makes it interesting to see where the people you meet are from. Beyond that, it's not safe. Teach them to never share their last name. If their first name is unusual, you might even pick an online nickname for them to give out as an extra precaution. Don't share emails, and don't visit webpages you hear about in game. These cautions will be obvious to any parent who plays online games. It makes you more aware of the dangers that must be avoided.