Hilary Duff joined her sister, Haylie, and parents Rob and Susan on a family vacation in Mexico yesterday. The ladies took a casual stroll around their resort but kept their bikinis covered up under brightly colored caftans. Hilary showed off a hint of her post-baby bod and has recently been hitting the gym with celebrity trainer Harley Pasternak. She's not the only actress who has been focusing on fitness in recent weeks; Jessica Simpson has also been hitting the gym. They've been keeping fans up to date on their babies, though, with Hilary sharing Luca's cute milestone moments on Twitter and Jessica posting a new photo of her pride and joy Maxwell on Facebook.