"Well, that was the fastest year of my life," Cavallari, 28, captioned a photo via Instagram. "Happy 1st birthday to my little baby bull! I love u with all of my heart, wild man."
In the pic, Cavallari's youngest son has his back turned to his famous mom. Clearly paying more attention to his toys, he appears to be holding a giant stuffed animal while playing on a basketball court.
Cavallari and her NFL hubby, 32, are also parents to Jaxon's older brother, 2-year-old Camden. "[It's] really sweet seeing Camden love being a big brother. Plus, you're definitely more relaxed with the second one because you're not stressed out by questioning everything that you're doing," the fashion designer told Chicago's Michigan Avenue magazine in August 2014.
As for how many more kids she wants? "Before we had children, Jay and I both wanted four," she added. "Now we're thinking three, but we're just going to have to see how it goes. Right now the last thing on my mind is having another baby, but it is a ton of fun."