And the adorable girl arrived at her shindig in style!
Seraphina, the Afflecks' middle child, walked into her party with her parents at Kidville in L.A.'s Brentwood neighborhood, looking like a princess in a pink dress with sheer tutu, white cardigan, and pink shoes!
A woman carrying Seraphina's yellow birthday cake followed behind the family.
Argo star Ben looked every inch the movie actor, wearing a brown jacket with the collar up to ward off the southern California chill and carrying a box into the party. Mama Jen, who also raises two other children, Violet, 7, and Samuel, 10 months, with Ben, looked casual cool in rolled up skinny jeans, a work shirt, and penny loafers.
But their daughter was truly the star of the show today! A chalkboard with the announcement, "Happy 4 Birthday Seraphina" welcomed guests to the Kidville party.
Ben's actor brother Casey Affleck and his sons, Indiana and Atticus, were spotted amongst the crowd of friends and family members.
The superstar couple paid about a thousand dollars for the bash, which featured juice and pizza, games, and art projects for all the kids.