Garner, 40, held Sam's hand as he stood in the store with a big smile on his face. The tiny tot wore colorful little shoes as he took a few steps.
The actress and husband Affleck, 40, celebrated their son's first birthday on Feb. 27, shortly after Affleck's film Argo won the Oscar for Best Picture on Feb. 24.
In his acceptance speech, Affleck raved about his wife and mother to daughters Violet, 7, Seraphina, 4, and son Sam. "It's work, but it's the best work there is," the director said of their relationship. "And there's no one else I'd rather work with."
He further shared how much Garner means to him in an interview with Access Hollywood. "All marriages, all relationships to a certain extent, require your work. They require work and investment," he said. "We work on it together, we try our best. Nobody's perfect. I would be lying to you if I said that either she or I were. She's more perfect than I am, I can tell you that."