In every package of Rubies bikini bottoms shipped to customers, 13-year-old Ruby Alexander includes a postcard, handwritten in purple, pink or teal-blue marker.

“You are strong, brave, and extremely important,” she wrote in one last year. “Keep being you and don’t let anyone bring you down. I am transgender myself and can understand you.”

It feels “really nice” to write the postcards and connect with other transgender and nonbinary kids, Ruby said: “When they see the letter or the postcard, they feel really attached, like connected to it, and that it’s more special than the actual bikini bottom.”

In 2019, Ruby’s dad, Jamie Alexander, founded the Rubies swimwear line for girls like her: transgender, nonbinary and other “gender creative” children who had trouble finding bathing suits that made them feel confident as well as physically comfortable. The line, named for his daughter, was created out of necessity, according to Alexander. Ruby wanted to start wearing bikinis like her friends, but Alexander and his wife were concerned about her sense of security in a potentially ill-fitting suit. When they looked around, they didn’t find many options that were suitable, particularly for bikini bottoms, Alexander said.

“There were none that were designed specifically for kids in mind,” he explained.

So Alexander, a tech entrepreneur, decided to make his own line of bikini bottoms alongside his daughter. The result is Rubies, which offers shaping bikini bottoms in black and pink. (A new line of shaping underwear and a one-piece halter swimsuit are also available for preorder.) More than being fashionable, the garments fill an urgent need among many trans and nonbinary kids and their families, who worry about discomfort, attracting unwanted attention or worse — being unintentionally outed.

For Rubies customers, the bottoms have been a game-changer.

One parent who bought a pair for his daughter, a competitive swimmer, wrote in a review, “her anxiety level is so much lower” — a change that apparently was noticeable to even her coach.

“My daughter says they look and feel amazing,” wrote another. “It was the confidence boost she needed.”

Fit clothing has been an ongoing issue for trans, nonbinary and gender-nonconforming people of all ages, advocates say. Men’s and women’s clothing are built with very specific builds and body types in mind, which can exclude a lot of cisgender people, as well as buyers who are gender-nonconforming. This is especially true, many say, for swimwear and intimate apparel.

“If the swimwear doesn’t fit one’s body and body parts effectively, it can expose someone in a way that feels very, very uncomfortable and distressing,” said Mere Abrams, an educator and social worker who focuses on gender and transgender health.

This can be compounded for young people, who may already struggle with acceptance. Attending a pool party, joining a swim team, going on a family vacation or meeting a physical education requirement can become fraught for trans or nonbinary kids, who may not feel safe or secure participating because of an ill-fitting suit.

“They really can’t be fully present and engaged in those activities,” Abrams said, adding that a lack of appropriate swimwear options is a big enough barrier that some young people will skip out on water sports and activities altogether. Trans and nonbinary youths are also bullied at higher rates than their peers, and locker rooms and bathrooms are often the settings for this type of mistreatment, violence and harassment, Abrams said.

And the issue may be more pressing than ever before, as Gen Z is notably gender diverse. According to a 2020 Pew Research report, Gen Z-ers are much more likely than those in older generations to say they personally know someone who prefers to go by gender-neutral pronouns, with 35 percent saying so, compared with 25 percent of millennials.

Cathy noticed early on that her youngest child was uneasy in swim trunks. During trips to the pool as a Cub Scout, her first-grader was reticent to change in the locker room with the rest of the group.

“They just couldn’t do it,” said Cathy, who is being identified by her first name to protect the privacy of her family. It wasn’t until her child came out as nonbinary at the age of 12 that Cathy fully understood why they were so uncomfortable having their body seen, she said.

Her child is 16 now, and Cathy can count only two times her teen has gone swimming since they were 12 years old. That includes a pool party, thrown by a local support group for families of trans youths.

“That was the first time in three years that my kid had been in a swimsuit, because there were other kids there that were all just like them,” she said.

One of her kid’s concerns is making sure their breast inserts don’t fall out when they’re in the pool. They’re also worried about swimsuits being too tight below the waist, and not giving adequate coverage when roughhousing or playing with friends. Mostly, Cathy’s child doesn’t understand why swimwear has to be so gendered at all, she said.

Because finding adequate swimwear has been so challenging, the easiest thing for the family is to avoid any situation involving swimsuits, Cathy said. This has meant pausing family beach vacations to Florida, like the ones they used to take. Cathy has also been fighting to repeal a mandate from their local school district that requires high school students to take a one-week swimming course to pass physical education. Because of the pandemic, her teenager was able to do remote-only learning and get around the requirement this year — a bit of relief for which Cathy is personally grateful, she said, although she knows the rule will continue to pose challenges for other trans and nonbinary youths.

She only recently learned about the Rubies line, but she’s delighted to see it, she said — and hopeful for the potential it could have for children like hers.

“If we could find something that my kid’s always comfortable in, are you kidding me? We would be going to the beach in a heartbeat,” she said.

Jennifer Solomon, the founder of the South Miami chapter of PFLAG, the nation’s largest organization supporting queer, trans and nonbinary people and their families, said the issues that swimsuits pose for transgender and gender-nonconforming people are persistent.

Solomon’s 10-year-old son, Cooper, identifies as a boy but expresses his gender in very feminine ways, she said. He always had a strong sense of who he was and what he liked: sparkles, vivid pinks, rainbows, makeup, all the “stereotypical girl” things. She recalled one story, when Cooper was much younger. The pair were walking through a children’s clothing section, and Cooper gravitated toward a bright, sparkly dress. Curious, Solomon asked him, “Why do you like that outfit versus a boy outfit?”

“He looked at me and said, ‘Momma, because that one’s beautiful,’ ” Solomon said.

After seeing him persistently pulled toward girls’ clothing and accessories, Solomon googled his behavior, and learned about the high rates of suicide among gender-nonconforming youths. Right then and there, Solomon said, she made a decision.

“I wasn’t going to be my child’s first bully. I was going to see and embrace my feminine boy for all the beautiful things that he is,” she said.

The Solomons are avid beachgoers, but finding the proper suit for Cooper has been challenging. In the past, they’ve opted for a swimsuit bottom with strategic ruffles around the waist, “so he could wear it and feel fully confident that he was covered,” Solomon said.

Solomon said she’s heard of other parents who have either bought suits with extra padding, or added additional padding themselves. But those suits can look and feel “like a diaper,” according to Solomon. He’s also outgrown his well-loved rainbow bikini with a red, ruffled bottom, and now sports a more “sophisticated” black one, she said.

Solomon is excited about the options the Rubies line can give her family, as well as the brand’s increasing visibility.

“It’s all about building that community and having parents see this [and] know that they’re not alone,” she said.

This has been a large part of Alexander’s work with the Rubies brand. He said he and his daughter will often field questions from families in places where there isn’t a lot of local support for trans and nonbinary kids. They’ve also leaned on their community of customers to help improve their products, working in input from kids and parents alike. As word has gotten out about their brand, more adults have also flocked to pick up their products, which are available in larger sizes, Alexander said.

Abrams, the social worker, noted that community is essential for gender-nonconforming youths and their families.

“There’s a lack of research and there’s a lack of awareness. One can’t necessarily turn to Google to find the things that are going to support their family and their young person,” Abrams explained. Instead, many lean on community knowledge to navigate challenges big and small.

Abrams, who uses they/them pronouns, is struck by another facet of Rubies’s approach to business: Its focus on making the young person feel good.

“That is really important because we live in a world where gender can be highly politicized,” they said.

Ultimately, the conversation should be more than just swimwear, and more than just kids, advocates say. Abrams said that they believe the fashion industry would do well to follow Rubies’s example for all transgender and nonbinary people.

“The fashion industry as a whole plays a really big role in trans liberation and gender inclusion, because for folks to feel comfortable in their bodies in the world, and for folks to feel like they can authentically express themselves, they really need access to products and apparel and underwear and swimwear that help them do that effectively,” Abrams said. “I think the fashion industry underestimates its role in supporting this community.”

Ruby has the kind of smile that is so big and bright you think you can see all her teeth. She is quick to flash it, braces and all, but when she talks about the way kids’ clothing is laid out now, it disappears.

Recently, she furrowed her brow as she described walking through a store like Walmart and seeing girls’ clothing on one side, boys’ on the other.

“I think it’s really annoying,” Ruby said. She wants to live in a world where those clothes don’t have to be labeled at all. To her, that world doesn’t seem so far off.

”Maybe, I don’t know, like a few years from now at least, that’s going to change," she said.

Editor’s note: An earlier version of this story incorrectly referred to Cooper as “Connor.” We regret the error.