Blue Ivy is the "best big sister" with twins Rumi and Sir Carter, says a source

Add being a dutiful big sister to Blue Ivy‘s budding resume, which already includes being a rapper and future style icon.

A source tells PEOPLE that the 5-year-old has been doting on her newborn siblings — twins Rumi and Sir — and even assists mom Beyoncé and dad JAY-Z with daily baby duties.

Credit: Theo Wargo/Getty Images

“Blue is the best big sister,” says the source. “[She] helps Beyoncé every day.

“Everyone is doing great,” adds the source. “They are still enjoying the summer in Malibu. Blue is excited to be back in school soon. The babies are growing and very cute.”

News of Blue Ivy’s sister skills confirm what 63-year-old grandmother Tina Knowles Lawson told Entertainment Tonight in July: “She’s a good big sister, she really is. She cares for them a lot.”

JAY-Z and Beyoncé welcomed their twins on June 13, according to birth certificates obtained by PEOPLE.

The parents quickly filed papers to trademark the apparent monikers for everything from fragrances and cosmetics to baby gear, tote bags, and water bottles.

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The family is currently living in a $400,000 per month rental home in the beach city, while looking for a permanent home closer to Blue’s school.