In the United States, reports of migrant children being separated and put into detention centers at the American border with Mexico pushed President Donald Trump to reverse the policy. The children were being held as their parents were being prosecuted for crossing the U.S. border illegally as Trump's zero tolerance border policy means any migrants crossing into the US face criminal charges.

In the EU, French government spokesperson Benjamin Griveauy said that the European Union and France "do not share the same model of civilization" as the US. He also said seeing the migrant children kept in large wire cages as "shocking."

In the EU it is not prohibited to detain grant children, as long as the detention centers are kept to certain standards.  "In all actions relating to children, whether taken by public authorities or private institutions, the child's best interest must be a primary consideration," Article 24 of the EU charter of Fundamental Rights states. It also says that "Every child shall have the right to maintain on a regular basis a personal relationship and direct contact with both his or her parents unless that is contrary to his or her interests."

"Detaining children for migration management or asylum reasons without family members is difficult to justify—and clearly not in the child's best interests," the European Union Agency for Fundamental Rights said last year.

Is detention in the child's best interest?

According to the United Nations Human Rights Office of the High Commissioner, EU currently stipulates that migrant and asylum-seeking children may be placed in detention, as a last resort, if is is in their best interests. Yet Renate Winter, the Chair of the UN Committee disagrees: "The claim that detention is necessary to protect children from going missing, being exploited or 'absconding' is misguided. Detaining children, whether unaccompanied on the basis of their or of their parents' immigration status, is never in the best interests of the child and constitutes a violation of the rights of the child," she said.

The UN Refugee Agency UNHCR has pointed out that "recent studies have indicated that detention of children can undermine their psychological and physical well-being and compromise their cognitive development. Furthermore, children held in detention are at risk of suffering depression and anxiety, and frequently exhibit symptoms consistent with post-traumatic stress disorder such as insomnia, nightmares, and bedwetting."

 In the EU, a 2016 Human Rights Watch report pointed out that Greek authorities detain children in policy custody often without "critical care and services" such as as the lack of counseling and legal aid. Many of the children, according to HRW. lack the opportunity to speak to the police without an interpreter. HRW claims "that the unjustified detention of children for prolonged periods amounts to arbitrary detention and violates children's right to liberty."