Every once in a while a law comes to light that so contradicts modern social mores, it’s very existence is shocking. Such laws, banning things like crossing the street on Sundays, are usually artifacts of a bygone time and so minor in scope that no one bothers to go back and undo them.

Massachusetts’ law on child marriage — actually the absence of such a law — would seem to fall into this category. The state allows children of any age to marry provided they have parental permission and the endorsement of a judge. With all of the right approvals, a child can legally wed before they’ve learned algebra or their state capitals.

But what would seem a byproduct of a time when people wed and started families at a younger age — or maybe our legislators’ deference to religious tradition and parental values — in fact creates the opportunity for child abuse. Though child marriages are rare, they are not unheard of, and that we allow them at all is shocking.

Lawmakers in Massachusetts and New Hampshire who are now weighing legal minimums for marriage should make it 18. Even that tender age is far too young to wed, most adults would agree, but it at least coincides with a legal standard of adulthood. Significantly, a teenager married at 18 could legally seek an annulment or divorce or protective order against an abusive spouse — something a child younger than that age could not do by themselves.

Truth be told, child marriages do not happen often, but they happen often enough. In Massachusetts, Department of Public Health data from 2000 to 2014 show about 80 nuptials a year involving a child.

An Associated Press report earlier this year suggests a number of cases of child marriage, here and elsewhere, involve children brought into the United States for prearranged unions.

Though parents or guardians may have given consent, in this country or elsewhere, advocates against child marriage say it really isn’t consent. A large number of the cases involve girls raised in poverty who are marrying adult men. Fraidy Reiss, who leads the advocacy group Unchained at Last, says families are coerced into making the arrangements for their daughters. Things go downhill from there.

“They are subjected to a lifetime of domestic servitude and rape,” Reiss tells The Associated Press. “And the government is not only complicit, they’re stamping this and saying, ‘Go ahead.’”

And it’s not just Massachusetts and New Hampshire. Eighteen states have no age restriction on brides and grooms, provided they have parental consent. Seventeen states, including New Hampshire, set the minimum at 16. (And New Hampshire only recently raised its age, which was previously 13 years for girls and 14 for boys. A bill filed earlier this year to raise the age again, to 18, was tabled, according to Reiss’ group.)

Why this situation persists is a mystery. The strong lure of culture and religion is a common explanation, yet we’ve managed to overcome the pull of tradition in writing and enforcing other laws that protect children from physical and sexual abuse.

And the evidence collected by groups such as Unchained at Last and Girls Not Brides shows that our laws’ silence leads exactly to that.

The United Nations Children’s Fund is among those advocating for a minimum age of 18 for marriage, in the United States and internationally. So far only New Jersey, where Reiss’ group is based, and Delaware have enacted that legal limit, and both only did so last year.

Massachusetts and New Hampshire, indeed every other state in the country, should quickly fall in line. What would seem a holdover from another time, when people generally got married at a far younger age, in our modern society can have devastating effects, abetting domestic violence and human trafficking.

Allowing children with limited legal rights to enter into marriage is a recipe for abuse.