What combination of characteristics defines something as either childish or for adults? Simplicity? Theme? Duration? Limited choices? Limited depth?
All of these, of course. But really; is this the list of characteristics of "children's board games" or "mainstream board games"?
If the mainstream press tells you that you should take a break from television and computer games in order to spend some quality time with your friends or family playing board games, what games do you suppose that they recommend? I'll give you a hint: it's not Civilization.
Honest to goodness, they recommend playing Candy Land and Sorry. Why? Because they are simple, have an unchallenging theme, don't take too long, present limited choices, and don't require too much thinking. So someone, either the mainstream press, or the game manufacturers, think that you're all children.
The only exceptions I've seen are in the theme department: party games, such as Taboo, Dirty Minds, etc. Not for children, no. For snickering young teenagers, perhaps.
There really is a spectrum of ambition among both children and adults. On one end of the spectrum is the child who takes an interest in something and wants to learn it. Self motivated. This type of child can play civilization building computer games, learns how to program both a web site and a VCR, and can probably beat you at chess. On the other end of the spectrum is the child who in uninspired, unmotivated, doesn't want to think, and doesn't get it. May have a wonderful personality or be the class clown. Either this child is slightly less intelligent, is tired, is not at all interested in playing right now, or has an attitude problem.
All of which sounds a lot like the adults I know.
In my opinion, games for adults are games for children. Games that we currently call "for children" are for no one. A child's first game should be checkers, fox and sheep, chinese checkers, or similar. Not Candy Land.