State officials report practical needs to put migrant minors in detention, and the European Convention on Human Rights sets legal limits on this practice. This article defines the scope of circumstances under which migrating minors may be detained by analyzing The European Court of Human Rights case law, using judgments in which the detention of migrant minors has been alleged a violation of Articles 3, 5.1, or 8. It also explores states’ needs for detaining such children, using data from 19 interviews with Swedish police officers, and compares these views with the case law. Police interviewees primarily describe two needs to detain children: to make deportations of children smooth and dignified, and to prevent minors from committing crimes. The investigation finds that migrant minor detentions are rarely permissible according to the Convention—especially under Article 3—and that the permissible scope is too small to meet the expressed practical needs. The actors involved in the issue of detaining migrant minors might have different perspectives on the issue, but they must not lose sight of the fact that these children are categorized as some of the most vulnerable in society and that their rights must be protected.