Kim Kardashian sent well-wishes to her son and "favorite boy" Saint West on his birthday. The 38-year-old "Keeping Up with the Kardashians" star penned a sweet post to Saint, her second-eldest child with husband Kanye West, on his third birthday Wednesday. Kardashian shared a photo on Instagram of Saint lounging in a pool chair. The toddler wears a White Sox t-shirt, athletic shorts and black Adidas sandals. "Happy Birthday to my favorite boy my Sainty Joon. I must have done something really special to deserve having you as my son. I love you to the galaxy and back," Kardashian captioned the picture. Kardashian's sister Khloe Kardashian and mom, Kris Jenner, also wished Saint a happy birthday online. "I love you Sainty Joon!!! Happy birthday!! they are growing so fast," Khloe wrote alongside a photo on Instagram Stories of herself with her nephew. "Happy Birthday to our adorable Saint!" Jenner captioned a slideshow on Instagram. "You bring so much love and joy into our lives! You are such a special, yummy part of my heart! We all love you so much!! #HappyBirthdaySaint." Kardashian is parent to Saint, 5-year-old daughter North and 10-month-old daughter Chicago with West. She told People in July her son is "obsessed" with Chicago and his cousins, including Khloe's daughter, True Thompson. "He is so obsessed with having a little sister. it is really, really cute," the star said. "They are all so good together, but I think Saint is probably most excited about all the babies," she added.