Hilary Duff and Luca Kisses for baby Luca! Hilary Duff and her sister, Haylie Duff, took Hilary's adorable son Luca, 11 months, for a swim on Wednesday, March 6. The sisters, both wearing swimsuits with their hair pulled up, posed for a picture together in the water. Haylie cradled her nephew and they both showered him with kisses. Hilary, 25, posted the cute photo on Twitter and captioned the shot, "Waterbug." Haylie, 28, also tweeted, "Swimming with my Seester and Luca. Favorite way to spend an afternoon." Though he's probably still learning how to swim, little Luca has recently learned how to walk. "Well, I officially have a walking baby on my hands!" Hilary announced on Twitter Feb. 28 of her son with husband Mike Comrie. "It's hilarious . . . the wobble makes it look like he's 3 drinks in!"