Samuel's big sisters Violet, 7, and Seraphina, 4, also attended the ceremony at Garner's family church, Christ Church United Methodist Sunday.
People.com said Garner and Affleck celebrated their eighth wedding anniversary the night before with dinner at the local pizza parlor Pies & Pints.
"Ben and Jen like to come in when they're in town," the restaurant's owner, Rob Lindeman, told People.com. "They're just really solid people. They seemed like they were having a great time."