Dragon Quest VI: Realms of Reverie isn't really good for younger kids due to the large amount of reading and the tendency to get completely stuck with where to go/beating a boss - therefore it's probably best left to the confident readers and more experienced players.
In Dragon Quest VI, you and your companions are able to travel between two separate, but connected, worlds - the real world and the phantom world - and completing certain tasks in one world will directly impact the other. In a vision you're character was warned of an incoming disaster, where a greater evil would take over the world - and it's up to you to put a stop to it before it's too late.
Dragon Quest is a role-playing game, where you and your party wonder from town to town across the worlds, defeating bad guys along the way. But there's more to it than that - often you'll need to talk to the various villagers to work out where you're going - and some of them will just want your help with simple tasks like fetching their ring from down a well.
In the turn-based battles, you and your party take it in turns to defeat the enemies - earning gold and experience points when you do. The gold can be spent on new equipment, and collecting enough experience points will make your character level up, making you stronger by giving you boosts to stats like attack and defence, as well as increasing your health.
Dragon Quest VI: Realms of Reverie contains little in the way of mature content. There's nothing in the way of bad language, and what little sexual innuendo there is is so mild as to be almost unnoticeable ("C'mon! Shake it! Show me what you've got!"). What little violence there is is similarly mild, with no blood, guts or gore, as enemies simply flash when your character lands a blow, and vanish when defeated.