The character designs of popular manga artist Akira Toriyama is one of the reasons why Dragon Quest is what it is, and a buyer of the game would certainly expect to see his artwork on the box. This has nothing to with the game being specifically made for kids. His artstyle (unlike that of other mangaka) very European (having comic looking, deformed characters in an lighthearted, but essentially serious story is common in European comic art (example). In US comic strips there is a big gap between humorous and serious comic, with little in between.

So the US box art is exactly what an US gamer in 1986 would expect. However, in recent years thanks to Dragonball Z, Toriyama's style (although not his name) has gained more popularity in the US and Europe, and in Dragon Quest 8 his character designs adorn the boxart in both Europe and the US.

Incidentally, calling Dungeon Siege a European style CRPG, is a bit off the mark, I think. RPG-ing is a predominantly US development, and the they only European thing about it is the Tolkienesque (mis)use of characters from European folklore.

Gamertag: Custardo