Celebrity Parents Proud Mom Jessica Simpson Shares Sweet New Photo of Son Ace Holding His Baby Sister Birdie Birdie wears a blue rose-patterned zippered onesie by Posh Peanut for the adorable photo op By Jen Juneau Jen Juneau Twitter Jen Juneau is a digital news writer for PEOPLE since 2016. People Editorial Guidelines Published on June 4, 2019 03:45 PM Share Tweet Pin Email Birdie Mae and Ace Knute are redefining the brother-sister bond! Jessica Simpson‘s middle child and only son, who turns 6 this month, was all toothy grin in a new photograph the singer shared to Instagram on Monday, cradling his baby sister in his arms. Baby Birdie, 11 weeks, didn’t look too certain about her position, looking off to the side with an inquisitive expression on her face. But she looked adorable nonetheless, wearing a blue rose-patterned zippered onesie by Posh Peanut that retails for $36 on the company’s website. “#BIRDIEMAE #ACEKNUTE,” Simpson, 38, captioned the cute snapshot. Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Parents newsletter. Jessica Simpson/Instagram Jessica Simpson Shows Off Impressive Supply of Pumped Breast Milk for Daughter Birdie Birdie has enjoyed many a bonding session with her brother, mom, dad Eric Johnson and 7-year-old big sister Maxwell “Maxi” Drew since the family welcomed her on March 19. Simpson’s two girls starred in a vintage-style image the singer, actress and fashion designer shared to Instagram last week, showing Maxi holding her baby sister while Birdie looked off camera in a sweet white and coral dress. “These ladies make my heart burst with love sprinkles 🧡,” Simpson wrote to accompany her post, adding the hashtags, “#MAXIDREW” and “#BIRDIEMAE.” RELATED VIDEO: Jessica Simpson Shares Adorable New Photos of 4-Week-Old Birdie with Daughter Maxwell and Son Ace Between his big-brother duties, Ace has been working on perfecting his game on the golf course. Late last month, Simpson highlighted her son’s skills on social media, with a video that showed him landing an impressive swing. “Already borrowing his dad’s clubs 💚#ACEKNUTE,” she captioned the clip, clearly proud of the youngster’s burgeoning athletic ability. But golf isn’t the only sport at which he seems to excel. Earlier in May, Simpson posted a photo of Ace on the baseball diamond, calling him the “homerun king.” And Ace’s athletic ability should come as no surprise, considering dad Johnson, 39, used to play in the NFL.