Reese Witherspoon made it a family affair on Saturday, March 9 when she headed out to a birthday party in Brentwood, Calif. with mom Mary, daughter Ava and baby son Tennessee in tow.

The This Means War actress kept things casual with a bright magenta sweater, jeans and leopard-print flats, while her lookalike daughter Ava, 13, opted for a breezy patterned white dress and jean jacket ensemble.

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Her younger brother Tennessee, 5 months, looked dapper in a tiny purple-and-green plaid shirt and white baby bonnet.

Witherspoon, 36, welcomed Tennessee to her growing brood on Sept. 27, her first child with husband Jim Toth (the actress is also mother to son Deacon, 8, with ex-husband Ryan Phillippe, who skipped the party).

The Oscar winner and CAA agent Toth, 41, tied the knot back in March 2011.

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"The kids met the baby the first day at the hospital," a source told Us Weekly shortly after Tennessee's birth. "Deacon is excited to have a brother. And Ava can't wait to babysit!"

In an interview with Chelsea Handler back in December, Witherspoon similarly praised her daughter's help around the house.

"She's so awesome!" she said of Ava's big sister skills.

This article originally appeared on Reese Witherspoon Brings Baby Son Tennessee, 5 Months, Lookalike Daughter Ava to Birthday Bash