Lorraine Weatherspoon and Elizabeth Taylor Quilliam of Michigan State University in East Lansing and colleagues examined 145 such sites with 439 food brands marketed. The children often see the game described in a publication or on food packaging and then go to the Internet to play the free game.
Quilliam said the children might miss that advertising is being used.
"They don't know that they're seeing an ad; they think they're playing a game, Quilliam said. "If they enjoy the game and the character, those positive feelings may translate to the product that is being advertised."
The found the websites typically promoted high-calorie and high-sodium foods as part of the game -- such as, "find three ice cream cones that match."
"We found a large proportion of foods that were unhealthy that were being marketed to children by these advergames," Weatherspoon said. "Not as many companies promoted foods that have multiple nutrients, things like fruits and vegetables."