Here’s some more anti-Nielsen fodder for Viacom CEO Philippe Dauman today at his UBS Global Media & Communications Conference appearance: The TV ratings company is admitting that it made a mistake when estimating the number of kids who are watching TV compared with last year. Though not directly related to Dauman’s fight with Nielsen over the ratings decline at kids network Nickelodeon, it’s likely he will use the admission for an I-told-you-so moment: The CEO has been on the hot seat since September, when Nielsen first reported the unusually weak ratings, and now he’s got ammunition for his claim that the decline is a “blip” owing to errors on Nielsen’s side. During the downswing, Viacom has seen analyst downgrades and a boost in make-goods that can’t be recouped during a time when Nick is ramping up its always robust fourth-quarter ad business, when it accounts for about 25% of Viacom’s ad revenue thanks to toy ads around the holidays. Nick also is losing traction to rivals like Disney Channel, which the week of November 20 beat Nick in the ratings for the first time since August 2007. Today, Nielsen is telling the Wall Street Journal that it is revising its estimate on the number of kids who watch TV: from up 1.7% to down 2.9%. The paper said Nielsen found that it failed to “apply a standard adjustment” after Viacom questioned the numbers, but that it has nothing to do with its measurements of Nick’s ratings. That matter remains before the Media Rating Council.