When Jonathan Sandhu takes his four daughters out in public, he knows people are going to stare.

It’s hard not to. Hannah, Lucy, Rebecca and Petra are identical quadruplets, a phenomenon doctors estimate occurs just once in 15 million births. There are roughly 72 documented cases of spontaneous identical quadruplets in medical history, a figure cited by physicians who have studied the rare phenomenon.

Still, Sandhu recently found himself laughing at one question in particular — so obvious that he made an Instagram video about it.

“Are there four of them?”

Yes. There are four.

And once that has been established, there is often a follow-up: “Are they twins?”

Apparently, Sandhu is not alone in fielding baffling questions from seemingly baffled bystanders. After he shared the video, people with experience of multiples chimed in.

“You crack me up! The question I always got was if ‘my twin brother and I are identical’ (I am female) I would answer. No, he has brown eyes,” one person commented.

Sandhu’s girls, now 2 years and 4 months old, may look nearly indistinguishable, but their personalities are already unmistakably their own.

Hannah, the oldest, is the boss. She tells her sisters when it’s time to sit down or go to bed. Lucy and Rebecca are the easygoing ones, happy to go along for the ride. Petra, the youngest, is the firecracker — “by far the most fiery, the most defiant,” Sandhu tells TODAY.com.

Their bond is just as striking.

Recently, Sandhu caught the girls hugging and kissing one another. They had been at it for about a minute before he stopped what he was doing to film them. On family walks, if one sister falls behind, he sometimes calls her name. If she doesn’t respond, he’ll jokingly say goodbye and keep walking, prompting the other three to race back for their sister.

“They’re just so distraught at the thought of their sister being left behind,” he says.

The girls are growing up in a busy household in Texas. Sandhu and his wife, Mercedes, both work full time as engineers and are raising the quadruplets alongside their two older sons, Luke, 6, and Aaron, 3.

For strangers, four identical toddlers can seem almost surreal. For their brothers, there is nothing particularly remarkable about it. The boys have grown up with four little sisters and are, Sandhu says, “still so in love and proud of them.”

Sandhu has noticed that people also react differently when he is out with the children alone without his wife. Strangers sometimes treat the outing as though he has accomplished something heroic.

“You would think I just saved the world,” he says. “The bar is so low for dads.”