Idaho Gov. Brad Little signed a bill barring gender-transition procedures for those under 18, making his the 14th red state to enact age limits as the debate over transgender rights and medical consent rages in state legislatures.

The Vulnerable Child Protection Act prohibits medical professionals from prescribing puberty blockers, cross-sex hormones and surgeries intended to align a child’s appearance with their opposite-sex gender identity, an issue gaining national attention amid a surge in children’s gender clinics.

In his Tuesday signing statement, the Republican Little warned legislators to tread carefully when overriding the will of parents.

“In signing this bill, I recognize our society plays a role in protecting minors from surgeries or treatments that can irreversibly damage their healthy bodies,” Mr. Little said. “However, as policymakers we should take great caution whenever we consider allowing the government to interfere with loving parents and their decisions about what is best for their children.”

The legislation, which passed overwhelmingly in the House and Senate, takes effect in January. Doctors found guilty of violating the law could be charged with a felony and face up to 10 years’ prison.

LGBTQ advocates who had urged Mr. Little to veto House Bill 71 accused him of turning his back on parental rights by placing age restrictions on “gender affirming care.”

“We are heartbroken for the families of Idaho today. We are watching parental rights being dismantled in the name of stigmatizing and harming our most vulnerable youth,” said Chelsea Gaona-Lincoln, executive director of the transgender-rights group Add the Words, Idaho.

Eleven states have passed laws and an additional three have enacted administrative restrictions on gender-transition treatments for those under 18, according to the American Principles Project.

Not all of the measures are blanket bans. Arizona approved a law last year banning “irreversible gender reassignment surgery” for those under 18, but not drugs.

Terry Schilling, president of American Principles Project, said it was “encouraging to see lawmakers nationwide taking action to protect children from the predatory transgender industry.”

He added, “The vast majority of Americans recognize that children are too young to consent to these procedures, which will have permanent, potentially destructive consequences for their long-term health. It is a massive scandal that such treatments are being offered at all, and legislators are fully justified in putting a stop to it.”

Last week, West Virginia Gov. Jim Justice signed a bill requiring two medical professionals and parents to consent to gender-transition treatments for minors. The APP did not count the law on its state tally.

Democrat-controlled states have swung back with proposals guaranteeing access to such treatments and protecting parents and doctors from prosecution. California became the first state to pass a “transgender sanctuary state” bill last year.