In the last decade and a half, a silent pandemic has spread among American youth: gender dysphoria and a radical medical experiment billed as its proper treatment. California is now poised to become a super-spreader—and confused children and their parents across the country will be the victims.

Gender dysphoria is a feeling of alienation between one's internal sense of "gender" and one's biological sex. Such feelings tend to resolve in 80 to 95 percent of kids if they are allowed to go through puberty unimpeded. But now, many kids are being fast-tracked to permanent body alterations called "gender affirming care."

This epidemic of the mind and spirit is not spread by contact or close quarters but by social media "influencers" and ideologues who have captured schools, medical groups, and state legislatures. In many states, teachers and government officials will encourage a child's claimed "gender identity"—whatever that child's sex—even behind parents' backs.

This treatment often starts with changed names and pronouns. It may then move to experimental puberty blockers, then cross-sex hormones and sterilizing surgeries. Double mastectomies, castration, and hysterectomies are just the beginning of this medical parade of horribles.

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These drugs and surgeries can cause severe pain; permanent sexual dysfunction; long-term damage to bones, heart, and blood circulation; and sterility. And there's no good evidence that they improve kids' mental and emotional health.

Rather than face these facts squarely, some states, such as California, are now so far gone that parents can lose custody of their daughters and sons for resisting this effort to upend natural puberty.

Instead of fighting this contagion, California's legislature wants to spread it to every state. Senate Bill 107 now sits on Gov. Gavin Newsom's desk. If it becomes law, California courts will have the power to strip custody from parents, wherever they live, who doubt the wisdom of these experimental and irreversible procedures—if their child so much as steps foot in California.

The primary victims of this policy, of course, are the children. But it's also an egregious attack on parents' fundamental rights, which include the right to direct their child's mental and physical health care.

This bill mandates that doctors conceal a child's medical information from parents if it is related to "gender identity" drugs and procedures, even if that information is sought under a court-issued subpoena.

It would also allow California doctors to treat minors still in other states. With the advent of telehealth, a child could get a prescription for hormones from a California doctor while at home in Arkansas or in Florida.

But the Arkansas legislature has passed a law to protect minors from the danger of cross-sex hormones. And the Florida Department of Health found that these procedures failed the strict standards we expect for medical care.

This digital workaround violates both parents' rights and state authority. The U.S. Constitution's "full faith and credit" clause requires states to defer to each other's laws and jurisdictions. California is thumbing its nose at other states' authority and jurisdiction.

Imagine the parental nightmares this California bill would unleash. A mother in Texas who has sole custody of her daughter could find her custody stripped by a California court who sides with an estranged father who takes the daughter to California to get puberty blockers. No family is off limits, and no court decision is safe, because California has decided that its courts—not those of the family's home state—should be the final deciders of whether parents are fit to raise their child.

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Worse, California is luring minors who believe they were born in the wrong body to abandon their families.

The state legislature knew what it was doing. When SB107 was being debated, Californian Chloe Cole testified against it. She came down with an acute case of gender dysphoria as a 12-year-old. She found out the hard way that the promises of puberty blockers, cross-sex hormones, and a double mastectomy at age 15 were lies.

The California assembly didn't listen to Chloe. Nor did it consider the testimony of the growing army of physicians and scientists, as well medical authorities in the U.K., Sweden, and Finland, who question the value and ethics of "gender affirming care."

Parents from across the country are joining that army. Many have urged Governor Newsom to veto the bill before it goes into effect on Oct. 1. If he fails to do so, Americans must stand for the safety and well-being of their kids. That means working to preserve the fundamental rights of parents and the authority of their own states to protect those rights.