The issue here is your tendency to take things people say on the internet at face value. For example, when a poster said

It's perfectly reasonable to consider children essentially sexless. Girls and boys are not yet women and men. They're distinct but until puberty the distinction is minimal.

You read every word in that post the most literal way possible & took it as the gospel truth. When, in fact, what that poster said is not actually, precisely true - something I suspect most readers understood, but which you chose not to.

Worse, you then rephrased what that poster said in a more extreme way, pretending what he or she really meant was

that children have no sex until puberty, there is no such a thing as a female or male child until puberty

Which I don't think is what that poster really meant after all.

In fact, human beings have a sex from the moment of conception. Sex differences have been observed & recorded in human placental cells five days post fertilization, and in the metabolism of human zygotes fertilized in labs via IVF earlier than that. Human sex differences precede the development of gonads in utero.

Those of us who have had prenatal testing when pregnant know full well that many of the fetal abnormalities tested for are sex-linked. Same goes for a number of the conditions that babies in the US, most of Europe & many other places are routinely screened for through mandatory blood draws & genetic testing shortly after birth.

Once children are born, there are thousands of physical differences in male & female human beings that are relevant medically and in terms of hygiene & safety from the get-go. The growth & development of infants is closely monitored & charted, but the charts are different because the normal ranges for boys' and girls' weight, length & head circumference are different. Moreover, the rate at which boys & girls grow and gain weight are different too.

More care needs to be taken when diapering female babies after bowel movements because the location of the female urethra unfortunately close to the anus makes girls highly susceptible to UTIs from fecal contamination. This is not an issue when diapering boys because the male urethra is inside the penis - and the little penises of boy babies are far from the anus. However, getting sprayed on definitely is an issue when diapering baby boys, but not girls.

Toilet training boys & girls is different. Teaching boys & girls how to cleanse & care for their "privates"is different too.

Many of the same genetic and childhood diseases manifest very differently in the two sexes, and have different trajectories, treatments & treatment protocols depending on whether a child is male or female. Many diseases that occur or become apparent in childhood are sex-specific. And diseases that occur at the same rates in both sexes still affect boys & girls very differently because of the many differences in male & female physiology. An excellent example is cystic fibrosis.

Female babies & children mount stronger immune responses to vaccines, and thus have more "side effects" than males.

Kids get tummy aches all the time. But when there's serious abdominal pain such that acute appendicitis is suspected, the assessment procedures & criteria are entirely different because the two sexes have different internal organs. For girls, the possibility of pregnancy, ectopic pregnancy, ovarian cysts, uterine issues have to be taken into account.

Because boys' gonads are external, very exposed & easy to injure, boys have to be taught to protect themselves in play & sports - and they need to be equipped with cups when they do contact sports. At the same time, girls of all ages are more susceptible to concussion than boys are, and need to be trained and equipped accordingly.

If a nine-year-old boy tells his parents or teachers that there's blood in his underwear, the appropriate response is to get him to a doctor pronto. If a nine-year-old girl does the same, the appropriate response is further inquiry and - most likely - showing her how to use sanpro.

Youth athletic records show that boys outperform girls in most sports long before the puberty of adolescence begins.

Read up on the physical development of males and females in utero, in infancy and in childhood, and you'll find that there are many, many important biological differences between boys & girls long before the puberty of adolescence kicks in. After all, the puberty of adolescence is actually the second puberty children go through. The first one, aka "the puberty of infancy," occurs from the end of the first month after birth into or through the six month.

The youngest girl on record to have given birth was 5 years old, 7 months at the time. It's a travesty to suggest that she was sexless.

Those are some of the facts on which I base my argument.