Sarah Michelle Gellar: I Took Two Kids on An Airplane – Alone

Sarah Michelle Gellar‘s son Rocky James will celebrate his first birthday in September, the same month daughter Charlotte Grace turns 4, but the actress only recently underwent an important rite of passage as the mother of two young children.

“The latest milestone I hit is flying with two children. It was my first flight with both children at the same time,” she tells PEOPLE, happily adding it went well. “I think that nobody on the flight would complain. I think that they were all very happy. I didn’t poll them afterward, but I was tempted.”

Luckily, both kids were easily occupied during the flight, either sleeping or playing with each other.

“[Charlotte] pretended to be the pilot,” Gellar, 36, says. “She told everyone to sit in their seats and buckle their seatbelts constantly, which was pretty funny. Whenever the light went on, she decided that she had to tell everyone just in case.”

And when it came time for the toddler to look after her younger brother, she rose to that occasion, as well.

“You could see in Rocky’s eyes that his sister is the highlight of his life,” says the actress. “She just adores him. She will tell anyone who will listen that she has a younger brother named Rocky. She’ll tell them what he likes, what he doesn’t like.”

In addition to mastering flying, Gellar is also learning how to juggle mommy time and her new work schedule for the upcoming CBS series The Crazy Ones, on which she costars with Robin Williams.

“It’s so fortunate because I was the hero,” she says of being able to bring Charlotte and Rocky to set. “My daughter was so excited to meet the man with all the friends. That’s what she calls Robin Williams because he sings the song ‘Friend Like Me’ [from Aladdin].”

But as luck would have it, Kelly Clarkson was also working nearby that day, and once Charlotte laid eyes on her, Williams lost some of his appeal.

“Once she met Kelly and Kelly was around, my daughter was no longer interested in the man with all the friends,” Gellar says. “I felt so badly because he was so excited. Thankfully, Rocky was so in awe of Robin that I think Robin got over it, but he did feel very second fiddle to Kelly Clarkson.”

When not shooting the series, Gellar has also contributed her time to backing a new awareness campaign called The Sounds of Pertussis, which advocates for vaccination against the ailment, better known as whooping cough.

“What I think that people don’t realize is that most times it’s passed on to a child, it’s by a family member and 50 percent of the time it’s passed on by the parents,” Gellar says. “These little infants, their immunity is not at the level ours is, so it’s our job to protect them. The last thing we want to do is bring something to them that could be potentially fatal for them.”