The trio appeared to be in good spirits in the photos (published by The Daily Mail, which you can see here), with Witherspoon, Phillippe and their youngest child together all rocking casual ensembles as they strolled around Los Angeles.
This marks one of the few times Witherspoon, 42, and Phillippe, 43, have been photographed together since their divorce was finalized in June 2008.
The former couple tied the knot near Charleston, South Carolina, in June 1999, after meeting at the Big Little Lies star's birthday party in March 1997. The two announced they were separating in October 2006. In addition to Deacon, they also share one daughter, Ava, 18.
Both have since moved on from each other. Witherspoon married talent agent Jim Toth in March 2011, and the two welcomed a son, Tennessee, in September 2012.
It appears Phillippe is currently single, but following his divorce from Witherspoon, he struck up a brief relationship with model Alexis Knapp in 2010. They share one daughter together, 7-year-old Kai.
In various interviews with ET, Witherspoon and Phillippe have both revealed how they've learned to master co-parenting over the years.
"We trade off," Phillippe told us in November 2016, when asked how they co-parent around the holidays. "You have to get to that point as a divorced parent, as any parent, where you're not putting yourself first. You want the kids' experience to be its own and not like, 'Well, I need to have my time!'' We have been very good about that."
Witherspoon agreed, sharing a similar story last September. "I would never change anything," she said in an interview with ITV's Lorraine.