Jennifer Garner Goes On A Shopping Spree...

But it's not for her slimmed down post-pregnancy figure -- it was for all three of her adorable kids!

Jennifer Garner was snapped perusing the wares at Pumpkinheads baby boutique in Brentwood this afternoon, and an eyewitness at the store tells X17online exclusively that the 40-year-old actress purchased apparel for baby Samuel and daughters Violet and Seraphina.

"She spent about half an hour checking out boys and girls clothing," our source tells us. "She bought tops, bottoms and a few sets of pajamas and she she was especially interested in the Daily Threads brand of children's apparel."

With hubby Ben Affleck busy shooting Runner Runner in Puerto Rico, looks like Jen's on her own when it comes to back to school shopping! Good thing she has a nanny to help her out every once in a while...