"Migration-related detention for children can never be considered... in the best interest of the child. There are always alternatives available," he added.
Over 100,000 children are being held in migration-related detention in the United States, including unaccompanied infants, and others separated from their parents before detention, said a UN expert in Geneva on Monday.
"Of course, separating children—as was done by the Trump administration—from their parents, even small children, at the Mexican-U.S. border is absolutely prohibited by the Convention on the Rights of the Child," said Manfred Nowak the lead author of a United Nations' 2015 Global Study on Children Deprived of Liberty, which found that the United States had the highest rate of children detained worldwide.
"I would call it inhuman treatment for both the parents and the children. And there are still quite a number of children that are separated from their parents—and neither the children know where their parents are and the parents [don't] know where the children are—so that is definitely something that definitely should not happen again."
In Mexico, the National Migration Institute found that 11,290 unaccompanied migrant children and teenagers have been processed so far this year, mostly from Honduras, Guatemala, El Salvador and Nicaragua.
According to figures from the U.S. Customs and Border Protection, at the end of the fiscal year in September, 76,020 minors were detained in that country, compared with October when the number reached 2,848.