They say that twins ought to have separate identities. They should be allowed to cultivate different interests, and to have different friends. But for a long time we didn’t take this advice seriously. Our twins seemed to enjoy being in the same preschool and playing together with the same friends. The typical Israeli Gan resembles a one-room schoolhouse – it is big open room with a small kitchen area and bathroom off to the side, and a back door leading into a large yard with riding toys, a jungle gym, a wooden house where the kids can hide and play “Mishpacha,” family – known in English as “playing house.” During recess at Gan there were only two places to be – inside and outside. Liav always preferred the corner with the dolls, whereas Tagel wanted to be upside down on the monkey bars. At night I read them the same books simultaneously on Liav’s trundle bed which pulled out from Tagel’s; they slept just like they were positioned in the womb – twin A on the bottom, twin B on top. Liav sat on the side closer to her pillow; Tagel sat closer to the foot of the bed, and each girl snuggled up beside me. We were all inhabiting the same fictional world, whether it was the cottage where The Seven Silly Eaters were preparing Mrs. Peters’ birthday cake, or the zoo where the otters and leopards were Wild About Books, or the treehouse where The Berenstein Bears were watching Too Much TV. When I turned the last page of the last book in the stack on my lap, it was as if we were all on the same plane that had just landed with a thud, jolting us back from the cottage or the zoo or the treehouse to a darkened room lit by a reading lamp with the door closed and the girls beside me yawning and pleading for just one more story.

Now it is different. In our new house the girls sleep on opposite sides of the room, each on her own twin bed elevated off the floor by a box spring. Sometimes I read them both picture books, but more often they read to themselves. Ever since first grade their social lives have diverged – they are in separate classes, they play with different friends during different recess periods, and after school they have separate playdates. And at night in bed reading, they no longer inhabit the same social worlds either. Their beds are lined not just with stuffed animals but with a new assortment of fictional friends who come to visit every evening between bathtime and lights out.

At first I assumed the girls would just share books. We are allowed to take out eight books from the library at a time – I figured that meant that each girl would read her books and then exchange them with her sister. But for the most part Liav was uninterested in any book that Tagel had already read, and vice versa. Neither girl wanted to enter into a world with which her sister was already familiar. At first I didn’t notice, because in any case only Tagel would agree to read with me; Liav read voraciously in Hebrew but refused to read in English, especially as Tagel increasingly found her stride. I was reminded of an earlier stage of their development when Tagel had begun crawling but Liav refused to move anywhere; Tagel used to fetch anything Liav needed while Liav sat there regally. Each evening Tagel was delighted to lie next to me in her bed and take turns reading pages with me in Ivy & Bean, a series about two best friends living a few houses over from one another on a quiet cul-de-sac in a leafy American town. Tagel fell in love with both friends, perhaps because she saw elements of herself in each of them: She is athletic and spunky like Bean, but also bookish and self-reliant like Ivy. If I were to draw a caricature of Tagel, she’d be reading while standing on her head, legs shooting high up against the wall and face obscured by an upside-down paperback of Ivy & Bean. It sounds, come to think of it, like an illustration right out of an Ivy & Bean book.

The illustrations are part of the genius of this series, because they not just decorative but explanatory. Each black-and-white line drawing is perfectly accurate, capturing all the details in the text such that the young reader who does not understand a part of the story can look to the accompanying illustration for the clue. The illustrations are a sort of Rashi’s commentary, illuminating the text but also adding more details to fill in the missing parts of the picture. Rashi, who lived in eleventh-century France, was the preeminent commentator on the Bible and Talmud. Sometimes he merely explains what is meant by a given word or phrase, but often he will round out a story by adding details from the literary exegetical literature known as midrash. Tagel has been known to pore over the illustrations with the intensity of a scholar poring over the marginal notes in a sacred tome, teasing out every last detail, like the erasers. Ivy and Bean have a collection of them – 56 erasers in different shapes that they use to play Eraser Valley, in which the various eraser figurines battle hurricanes, tsunamis, and other natural disasters. Tagel spent at least ten minutes examining each eraser in the drawing, and she wouldn’t let me turn the page until we each picked our favorites. She wanted Liav to weigh in as well, but Liav refused to set foot in Eraser Valley. Ivy & Bean was Tagel’s domain, and Liav wanted no part of it.

Eventually Liav agreed to start reading with me, but it had to be her own series. Ivy & Bean was Tagel’s social world; Tagel had already befriended not just the titular characters, but also the family members and classmates who comprise a cast of supporting characters in each of the books. We had plenty of Ivy & Bean books on our shelves, but if Liav were to begin reading in English, she needed her own series. I was transported back to that moment when we’d decided to separate them for first grade. Liav needed her own friends – she wasn’t going to tag along with Dusit and Emma and Sophie S. and Sophie W. and Ivy and Bean’s other classmates. (Sophie S. and Sophie W.! I love the ingenious verisimilitude of two characters with the same first name distinguished by the first initials of their last names, though the author of course has the whole name dictionary at her disposal. It is so true: Nearly every elementary school classroom has at least two kids with twinned names who have to lug around the first initial of their last names in order to individuate.)

Liav knew that if she entered Ivy and Bean’s milieu, she would always be known as Tagel’s kid sister. Tagel would be books and chapters and pages ahead of her, and Liav would forever lag behind. Tagel would know just how to annoy her sister; she would pretend she could hardly hold herself back from spoiling the endings and wink at me above Liav’s head to show off what she and I already knew but Liav had not yet read. Literary scholars use the term dramatic irony to refer to a situation where the audience knows more than the characters; Tagel would always know more than Liav and would lord it over her sister, twisting dramatic irony into cruelty. Liav wanted none of it. And so I found her a series of her own.

Instead of the quiet cul-de-sac of Pancake Court, Liav and I found a home for ourselves in an apartment building in Boston, where eight-year-old Clementine—the well-intentioned but troublemaking heroine of the eponymous series by Sara Pennypacker—lives with her father, mother, and young brother. We befriended Clementine’s best friend Margaret, though we both agreed she was a bit stuck-up and obnoxious sometimes. We laughed together at Clementine’s antics and cheered her on when she managed to shine against all odds. We both agreed that the best book in the series was the one about the class talent show, in which spunky Clementine—convinced that she has no talent whatsoever and therefore can’t participate in the show—ends up helping the principal run the entire production, thereby proving that she has talent after all. We agreed, lying there in her bed together, that sometimes the best talent is just being yourself and finding the way that you can be most helpful. I told Liav that she had an extraordinary ability to connect with her young sister – often she was the only one who could understand what was upsetting Shalvi and calm her down. That too is a talent, we agreed. Liav has many talents in the conventional sense, but we both took away from the book an important lesson: Sometimes the art you create is not something you sketch or perform but the arc of the life you live by just trying to be your best self, day in and day out.

At night I alternated between reading Ivy & Bean with Tagel and Clementine with Liav. Sometimes I imagined their bedroom was divided down the center, midway between their beds – Tagel’s side of the room was lined with the potions Ivy had concocted in training to become a witch; Liav’s side was decorated with Clementine’s drawings. When we had ample time to read, I traveled from Boston to Pancake Court as I made my way from one bed to the other, sitting in on Ivy and Bean’s classroom and then on Clementine’s, joining in on one family dinner and then the other. I tried to keep their friends straight, but sometimes I’d get confused, and Tagel would look at me with a puzzled expression when I jokingly referred to baby Yitzvi as Mushroom, and then I would remember that it is Clementine—Liav’s friend!—who teasingly refers to her younger brother by various vegetable names.

I didn’t always make up the pages I’d missed when the girls read on their own, but I tried always to check in so I was up to date. “Did Clementine get sent to the principal again?” I’d ask Liav on our walk home from school, and it wouldn’t seem at all strange to her that I was asking about a fictional character and not a member of the class with whom she had just spent the morning. “This reminds me of the secret spot in Ivy’s backyard,” I’d comment to Tagel when we found a quiet corner of the park in which to change Yitzvi’s diaper. These comments, though seemingly offhand, became a way for me to connect with each twin individually – a sort of secret language that only we shared.

The two series of books are not all that different; they both feature annoying siblings, misunderstanding teachers, friends who show-off too much, and parents who seem at times unfairly strict. But then again, Liav’s school friends are not all that different from Tagel’s; they gravitate to the same kinds of girls, and occasionally they all end up playing all together in the yard after school, blurring the class boundaries. Inevitably there are arguments about who is allowed to play with whom, and who is considered a closer friend. These arguments are normal and perhaps even salutary. But at least when it comes to their fictional friends, there is a clear divide: Clementine will never play in the backyard at Pancake Court, and Ivy and Bean will never ride Clementine’s school bus. Sometimes the best talent is being yourself, which can be hard for all children, and especially twins. I’m grateful that Liav and Tagel each has her own fictional space—small enough to fit into her side of the bedroom, but large enough to fill the expanse of her imagination—in which to daydream, develop, and discover her talents.