It was a fun-filled Saturday near San Francisco for a group of A-list celebrities who came together to celebrate the 40th birthday of producer Susan Downey, wife of Robert Downey Jr . Stars like Gwyneth Paltrow , Jason Bateman , Justin Theroux, and Gwen Stefani  were all on hand to ring in Susan's big day at a picturesque picnic spot by the bay. The pals mixed and mingled at a food truck as their kids played in the grass. Gwyneth Paltrow shared a sweet hug with her daughter, Apple Martin, while actress Maya Rudolph brought along her 3-year-old daughter, Lucille, and the baby daughter she welcomed in September. Justin Theroux, who showed up sans fiancée Jennifer Aniston , stayed close to Jason Bateman, and Jason even helped feed Justin a sandwich while they chatted. Gwen Stefani, who is currently pregnant with her third child, gushed over another partygoer's baby while her husband, Gavin Rossdale , socialized with the crowd.
Reese Witherspoon  and her family were also on hand for the event; she showed up with her husband, Jim Toth, and kids Ava and Tennessee and seemed to be enjoying herself while eating snacks and snapping photos. Reese and 14-year-old Ava even posed for their own mother-daughter photo — can you believe how much they look alike ? Everyone at the outdoor gathering looked to be having a blast — maybe Susan Downey can produce them all in a movie together?