Jessica Simpson celebrated her son's third birthday with her family on Thursday. The 35-year-old designer and husband Eric Johnson threw son Ace Knute a dinosaur-themed birthday party. The couple are also parents to 4-year-old daughter Maxwell Drew. "Happy birthday dinosaur! You complete me #3 #aceknute," the former reality star captioned a family photo from the fete. "Ace turns 3 and I feel prehistoric! #dinoparty." The mom-of-two dressed for the occasion in a matching palm leaf-print crop top and fitted mini skirt. The party featured plenty of dinosaur-shaped balloons, along with a volcano-shaped birthday cake. Simpson and Johnson started dating in 2010 and welcomed their daughter and son prior to marrying in 2014. The designer discussed the dynamic between her children in an interview with People in April. "She definitely lets her brother know that she's the oldest and that she is in charge," she said of Maxwell. "Ace is finally starting to stand up for himself." "[The kids are] always very chill in the car unless they're bantering back and forth," the star added. "Then me and Eric just have to tune them out. Just let them talk back and forth and get through it. They're brother and sister!" Simpson last released the holiday album Happy Christmas in 2010 and teased new music on Instagram in May. She also continues to oversee her Jessica Simpson Collection fashion line.