Scores of 'baby boxes' have popped up across Europe in the past decade where mothers can leave unwanted newborns anonymously. While advocates say the boxes keep babies alive, the U.N. is now alarmed at their rising numbers.

Ina Fassbender / Reuters A 'Babyklappe', with a sign 'Babywindow', is pictured at a hospital in Essen May 25, 2007. 'The 'Babyklappe', a baby drop box is a place where parents can drop off unwanted infants anonymously at several hospitals in Germany.

On the front door to the facilities of SterniPark, a children’s charity in Hamburg, Germany, there’s a steel door to a hatch where unwanted babies can be left anonymously. Once closed, it cannot be opened again from the outside. Established in 2000, this is the first of Germany’s now 80-plus babyklappe, or baby boxes or baby hatches, as they are known elsewhere in Europe.

The spread of these boxes across the continent, particularly in Eastern Europe and Germany, drew sharp criticism from the U.N. Committee on the Rights of the Child on Monday for contravening “the right of the child to be known and cared for by his or her parents.”

“Many NGOs and institutions use it as a cheap and populist solution to the problem of child abandonment,” Dr. Maria Herczog, a member of the UNCRC, tells TIME. “It is definitely a growing practice across Europe.” Herczog says she’s working towards setting up an E.U. seminar on the subject as she believes it’s a “cultural issue” which is being exacerbated by current budget cuts and the broader economic crisis across the continent.

The baby box’s roots go back to medieval times in Italy, where “foundling wheels” would be placed in homes so that women could leave their babies in secret rather than killing them.

The hatch’s popularity in recent times is most peculiar in Germany, the country with Europe’s strongest economy. SterniPark set up its first babyklappe following the discovery of a dead baby on a treadmill at a recycling plant. The charity now operates three hatches in Hamburg.

For baby-box advocates, the argument is simple: They help prevent infanticide and protect a child’s right to life. Roughly 30 to 40 babies die each year in Germany due to abandonment; SterniPark says that roughly the same number of babies have been left in the hatches since their inception. Only a small minority of mothers ever come back to claim their children.

Critics, however, argue that the boxes have no impact on infanticide rates and that many women do not give up their babies by choice. Herczog says evidence suggests that men or the mother’s relatives are frequently the ones leaving babies in the hatches, not the mothers themselves.

In the U.S., “Safe Haven” laws have been introduced in all 50 states allowing children to be left anonymously in designated places such as hospitals. These laws, first introduced in Texas in 1999, have naturally been controversial.

Nebraska ran into problems in 2008 when it defined children covered under the law as those under the age of 18 and parents began dropping their teenagers off at licensed hospitals. The law was swiftly changed to allow only babies less than 30 days old to be dropped off.

Though baby boxes are tolerated by the authorities in Germany, new laws may make it more difficult to leave children in them in the future. The Guardian reports that lawmakers earlier this year began discussing a new “legal framework for confidential births.”

The paper says the German constitution guarantees all citizens the right to “know of their origins” and fathers the right to be part of a child’s upbringing. “Both are breached when a mother gives birth anonymously,” the paper says.