I always assumed the trans flag was a rip-off of the striped Medline cotton flannel baby blankets that have been standard issue in US maternity wards and birthing centers since the early 1980s. Significantly, the 80s was when the two children fathered by the inventor-designer of the trans flag, Monica Helms, were born in the US. Unless they were born at home, it's a pretty sure bet that Monica's children were swaddled in the unisex Medline blankets with the pink and blue stripes routinely used in all health care settings for newborns back then:

https://www.medline.com/media/catalog/CA08/CA08_01/CA08_01_01/PF02620/PF02620_PRI01.JPG

BTW, trans flag inventor Monica Helms is on the right in this photo: https://www.flickr.com/photos/nationalmuseumofamericanhistory/14772026379/in/photostream/

More on Monica, who served in the US Navy as a machinist mate on a nuclear submarine in an era when such an option was not open to women:

In the early 1980s, I thought I was a heterosexual crossdresser. I was married, and I liked women. In 1987, a friend of mine and I were with a group of other crossdressers in San Francisco on what was called a “holiday in femme.” We’d go to cities for one weekend once a year. My friend told me why she was starting to transition, and I [recognized] all the same reasons in my head. She put together the puzzle, and I realized I needed to do the same....I started taking hormones in 1992. My kids were young, three and five. In 1997, I started living as a woman. The following year, my marriage ended.

Yet even though Monica believed Monica's self to be a heterosexual cross-dresser for the first 40+ years of life, Moncia has since retconned the story of Monica's childhood to fit the standard trans narrative that Monica really "knew" Monica was the opposite sex from an early age. To Monica's credit, though, Monica does not claim to have been exceptionally precocious as a child the way so many trans people do. Unlike El Page, who now claims to have been able to read and write - and to pen full "love letters" too - when El was a toddler just learning to stand an walk, Monica says such skills were absent even at the ripe old age of five:

I didn’t start to feel like a woman at a certain age—I started to feel like a girl. I was five years old, growing up in Arizona, and I prayed to God to turn me into a girl. You can’t tell me that this is a choice. What does a child in 1956, who’s five years old and can’t read, know about being a different gender? https://www.atlantamagazine.com/news-culture-articles/meet-the-navy-veteran-who-created-the-trans-pride-flag/

My response to Monica's last question is, If instead of focusing on your own cross-dressing and taking cross-sex hormones when your children were bairns you had focused on them, maybe you would have realized that all little kids imagine themselves to be things they are not, that wanting and pretending to be the opposite sex is quite common amongst children, and kids - and adults - pray to god for all sorts of impossible things. Like miracles.