Watch Jennifer Garner Sing Onstage at Save the Children's Centennial Celebration

Jennifer Garner had something very special for attendees at Save the Children's "Centennial Celebration: Once in a Lifetime" gala on Wednesday.

The 47-year-old actress hosted the star-studded evening, and during a visit to the stage, she broke into song. Garner sang a rendition of "Do-Re-Mi" from The Sound of Music, except the lyrics were altered to honor the organization's special occasion.

"Save the Children, one hundred years," she sang, while rocking an all-black ensemble by Lanvin featuring a large bow and stunning diamond necklace by Le Vain. "We have three lofty goals: A healthy start for kids, the opportunity to learn and always protect the young from harm."

"Perhaps you remember the commercials," she hilariously asked in her song. "Sally Struthers, some children and some flies. For the price of one coffee a day, you can save many children's lives in faraway places." When she finished, the audience erupted in applause. 

But that wasn't the only surprise of the night. Prior to the actress breaking into song, Drew Carey interrupted her monologue to present Garner herself with an award, stating she's "raised tens of millions of dollars for this organization… thank you for everything you're doing. God bless you."

Prior to taking the stage, Garner chatted with ET on the event's red carpet, where she shared her excitement for Halloween and admitted that her three kids aren't as easy to convince to don family costumes for the holiday as they used to be, now that they're getting older.

"It definitely gets harder," said Garner -- who is the mother of two daughters, 13-year-old Violet and 10-year-old Seraphina, and 7-year-old son Samuel, whom she shares with her ex-husband, Ben Affleck. 

"I mean, I remember one year when I talked both my girls into dressing up as pigs, and they were so cute!" Garner recalled. "And now they would be like, 'No, mom, oh my gosh, no!'"

"So yeah, it's harder. But they're gonna be cute, whatever they are," she added.

Garner, a trustee for Save the Children and one of its ambassadors, has been an outspoken champion of the organization for years. She communicated that passion with ET.

"When you are lucky enough to get to see a problem up close, and for me that is poverty in rural America…, and then you see a solution? And you see hope and optimism? There is nothing that is more of a driver than that," Garner stated.

See more from Garner's interview below.

RELATED CONTENT:

Jennifer Garner’s Kids Have the Meanest Nickname for Her

Inside Ben Affleck's Healthier Lifestyle and Relationship With Ex Jennifer Garner 1 Year After Entering Rehab

Jennifer Garner Says She Was 'Defined' by Pregnancies and Babies

Related Gallery

Must-See Celeb Sightings: September 30-October 6, 2019