The couple enjoyed a romantic low-key dinner at Bistro 82. "They were drinking red wine," an onlooker tells Us Weekly of the parents to Violet, 8, Seraphina, 5, and Samuel, 2.
"They looked relaxed," the source tells Us of the couple who dined at the French restaurant in Royal Oak. "No one was really bothering them at all -- they were really normal, they fit in," the source adds.
Prior to their celebration, Garner spent time with her three kids in her hometown of Charleston, W. Va.
"Jennifer sent her kids back to L.A. with a nanny," a second source tells Us of the 42-year-old "Draft Day" actress, who flew in solo to Detroit earlier Sunday to enjoy the one-on-one time with her husband, who is currently in the city filming "Batman vs. Superman: Dawn of Justice".
The pair tied the knot back in 2005 after falling in love on the set of "Daredevil". Garner was previously married to her "Alias" costar Scott Foley; Affleck was previously engaged to Jennifer Lopez.