The notoriously private couple was spotted out without their kids on a romantic walk this week.
For the causal outing, Song, 35, wore a white-and-red baseball T-shirt with wide-leg jeans and white sneakers. Culkin, 42, rocked shades and a chambray button-down shirt with black jeans and Converse.
Song was caught mid-laugh as she chatted with her longtime love.
The parents of two reportedly welcomed their second child, son Carson, shortly before Christmas 2022.
The pair are also parents to 2-year-old son Dakota. Song and Culkin met on the set of the 2017 film Changeland, and got engaged nearly a year after they welcomed baby Dakota in 2021.
As for the type of parents they are, Song gave some insight into their style while speaking to The Cut.
"My fiancé and I are very hands-on," she told the outlet of parenting. "We don’t have a nanny, but my mom has been here with us since my son was born... I think when you and your partner have kids, especially the first few months, you don't have the patience to be polite with each other. Being communicative when you need help is so important. Instead of having set duties, we just feel each other out. I'll be putting my son down and my partner is like, 'Let me feed the animals and get dinner ready.'"