Never tried it myself but I doubt it will be suitable for a young child.
Even if you put aside the monsters, demons, violence and other content typically included in such games (which can be ok if accompanied and handled properly by the parents) what makes it a real problem is that it is a MMORPG. Which means your child will be exposed to the type of crowd that often plagues the internet in general and massive multiplayer games in particular. This, under the anonymity of the internet and behind the mask of a virtual game identity, often translates into vulgar, obscene and abusive behavior.
Now, I guess this low profile and relatively unsophisticated game has by far less problem than games like World of Warcraft. Still, I would be reluctant to let my young child wander in these worlds, certainly not unsupervised.
I'd start with toontown 