A source tells ET that de Armas was 'very social with the kids.'
Ben Affleck and Ana de Armas enjoyed an afternoon out shopping together on Saturday -- with two of his kids in tow. An eyewitness tells ET that the group bought party supplies at Bonjour Fête at Palisades Village in Pacific Palisades, California.
"It looked like birthday supplies," the eyewitness tells ET, noting that "Ana was very social with the kids." "They also took a family selfie together."
It's unclear who the supplies were for, but Affleck's daughter Violet will turn 15 on Dec. 1. In addition to Violet, Affleck also shares 11-year-old Seraphina and 8-year-old Samuel with ex-wife Jennifer Garner.
Affleck, 48, and de Armas, 32, recently returned from New Orleans, Louisiana, where they did reshoots for their film together, Deep Water. The pair met on set of the movie, which initially wrapped filming earlier this year. Romance rumors sparked between them in March, when Affleck and Armas were spotted vacationing together in Cuba.
De Armas started spending time with Affleck and his kids in Los Angeles soon after, and by May, a source told ET that she had fit seamlessly into the family dynamic.
"Ben and Ana are happy together and have enjoyed spending time with his family," the source told ET. "He and Jen continue to work together on co-parenting. They make it work."
See more on the couple in the video below.
Reporting by Hiba Barry.