Jaxon turned six years old on Thursday, and Cavallari shared sweet pictures of her hugging him on Instagram to mark the occasion.
"Happy 6th birthday my little man," she wrote. "Jaxy, you have such a sweet, sensitive side yet have the ability to make everyone laugh with your incredible sense of humor and wit. You light up a room and make this world a better place. I'm so thankful to be your momma. Love you forever angel."
It's been a difficult time for the 33-year-old reality star, given her recent split from Jay Cutler after 10 years together. Aside from Jaxon, the two also share their 7-year-old son, Camden, and their 4-year-old daughter, Saylor.
A source told ET on Monday that Cavallari and the former NFL star want to keep it civil for the sake of their kids.
"Jay and Kristin are doing better as the couple has hammered out temporary custody for the time being and Kristin was able to buy the house she wanted in Nashville, not too far from their current house," the source said. "At the end of the day, Kristin and Jay want to make everything work for their children and they're still deciding what that looks like but know they need to remain a solid front."
For more on their parenting plan, watch the video below: