This site lists Barnyard for PS2 as a 4-player game, and so does Play.com from whence I purchased it. The packaging, however, says it's a one player game, and I can't find anything in the game to suggest it supports more than that.

Does anyone know anything about this? I've got four kids who would all like to play concurrently, but so far we've only managed one at a time.

Apparently it's only a 1-player game. The initial press release from which I got that product description detailed a 4-player set of minigames. They must have dropped that aspect of the game....