From Campaigning to Diapers: Chelsea Clinton Reveals How Hillary Is a Devoted Babysitter to Charlotte

When it comes to babysitting for her 11-month-old granddaughter Charlotte, Democratic presidential candidate Hillary Clinton is, simply, “Grandma Hillary.”

And she does it all, says her daughter, Chelsea Clinton: diapers, feedings, story time, sing-a-longs, even teething duty.

Most recently, taking the reins on Charlotte’s care came after a three-day campaign trip. “My husband Marc [Mezvinsky] and I were at a dinner for a friend who recently got a new job, and my dad was out with friends, so my mom babysat which was really nice,” Chelsea, 35, tells PEOPLE in an interview for the new issue on newsstands Friday.

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And with Charlotte’s seventh tooth coming in none too easily these days, Hillary’s tour of duty included “far and away the most popular song in our house right now, ‘The Wheels on the Bus,’ ” Chelsea explains with a chuckle.

“When Charlotte has challenges teething, ‘The Wheels on the Bus’ song can go on for hours. Like, everything gets on the bus — every animal from Old MacDonald’s farm gets on the bus, everybody we know gets on the bus, everybody in our family, all of our nieces and nephews and cousins, everybody and everything is on the bus. So my mom is very sweet when she’s singing ‘The Wheels on the Bus.’ ”

And, thanks to Grandma, whenever Charlotte hears “Twinkle, Twinkle, Little Star,” she mimics the twinkling of stars by scrunching her little hands open and closed. “It’s very sweet,” says Chelsea. “She learned that from my mom.”

RELATED VIDEO: Chelsea Clinton: I Love Watching Mom Sing to Charlotte

Chelsea spoke with PEOPLE in the offices of the Clinton Foundation last Thursday as part of the launch of her first book, It’s Your World: Get Informed, Get Inspired & Get Going!, a primer for middle-schoolers on issues like poverty, health care and wildlife conservation — and how they can get involved in making a difference in the world.

Chelsea says her mom and dad, former president Bill Clinton, always impressed upon her the importance of being informed, having an opinion and engaging in the world around her.

And now they are cutely determined to have a big influence on Charlotte, too — from checking in every day with Chelsea or husband Mezvinsky, to seeing Charlotte as often as they can, to dusting off Chelsea’s old favorite baby book, Each Peach Pear Plum, to read to their granddaughter, who turns 1 on Sept. 26.

“Watching them do all of that with Charlotte is just a lot of fun … an unexpected joy in this process,” Chelsea says. “They are so interested in everything about her — getting to know her and being part of her life and part of her daily route — so it’s not just checking in once in a while, but checking in every day to see how she’s doing. ‘What are her newest achievements? How’s she eating? How’s she sleeping? How many teeth does she have?’ ”

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Far from finding the parental involvement intrusive, Chelsea says “that’s what it should be” and teases her parents that they need not be coy about it all.

“Truly, this has happened now a few times, where my parents were just like, ‘Oh, I’m in the neighborhood. Can I come by?’ ” Chelsea says. “And I’m like, ‘You weren’t in the neighborhood. There doesn’t need to be a pretense.’ ”

Grandma Hillary was dead wrong about one thing having to do with her granddaughter.

Back in May, she jokingly predicted that Charlotte’s first words, after so much immersion in books, would be “Enough with the reading.”

In fact, Charlotte’s first word was “up” — always accompanied by outstretched arms asking that she be lifted, Chelsea says. “Up” was followed by “hi” and “bye.”

For more from Chelsea Clinton, pick up the latest issue of PEOPLE, on newsstands Friday.

— Sandra Sobieraj Westfall