Buzz·Posted on Oct 31, 2012First Look At Yahoo! CEO Marissa Mayer's Baby BoyThe new mom tweeted a photo of her beautiful baby boy, Macallister, as they attended YaBoo—the company's kiddy Halloween party.by Tommy WeselyBuzzFeed StaffLinkFacebookPinterestTwitterMail marissamayer @marissamayer One month old - Macallister and me heading to YaBoo, the children's Halloween party at @Yahoo! http://t.co/TNxVnV2K Tue, 30 Oct 2012 19:44:10 +0000 Reply Retweet Favorite One month old - Macallister and me heading to YaBoo, the children's Halloween party at @Yahoo! http://t.co/TNxVnV2K-- marissamayer