Hilary Duff was in a bikini yesterday for a vacation with her son, Luca Comrie, in Mexico. She's south of the border with Luca and other members of her family, including sister Haylie Duff and their parents, Rob and Susan. Hilary Duff's postbaby bikini body was covered up by a caftan earlier yesterday, but she showed skin in her two-piece later on for a dip with her son. Hilary and her husband, Mike Comrie, welcomed baby Luca earlier this year in March. She's since stuck close to home in LA to spend time with him and Mike, but also focusing on fitness with the assistance of trainer Harley Pasternak. Hilary's also got a new project to focus on. She's teamed up with Nikon as part of their Small Moments Are Huge campaign and is sharing even more pics of her adorable family.