Following the ECtHR’s Kanagaratnam, and Muskhadzhiyeva judgments, the Secretary of State decided that from 1 October 2009 onwards families with children that are arriving at the border and that are not removable within 48 hours after arrival should be accommodated in a family unit.
However, in August 2018, Belgium opened detention facilities for families with children. Article 74/9(3)(4) of the Aliens Act allows for a limited detention of the families with children in case they do not respect the conditions they accepted in a mutual agreement with the Immigration Office to stay in their own house, and/or absconded from the return homes. The closed centre for families is located next to the 127bis repatriation centre near the Brussels National Airport. The Royal Decree of 22 July 2018 (amending the Royal Decree of 2 August 2002) establishes the rules for the functioning of the closed family units near Brussels International airport.  While the Royal Decree was suspended by the Council of State in April 2019, the latter must still issue a decision on the annulation of the Royal Decree.
The current government has agreed that it can no longer detain children in closed centres, as a matter of principle. New, alternative measures will be developed to avoid that this measure would be abused to make return impossible. However, the government has not retracted the aforementioned suspended Royal Decree yet, the procedure to annul the Royal Decree is still pending before the Council of State.
The detention of unaccompanied children is explicitly prohibited by law. Since the entry into force of the Reception Act, unaccompanied children are in principle no longer placed in detention centres. When they arrive at the border, they are assigned to a so-called Observation and Orientation Centre (OOC) for unaccompanied children. This only applies to those unaccompanied children with regard to whom no doubts were raised about the fact that they are below 18 years of age and are identified as such by the Guardianship Service (see Asylum Procedure: Identification). Also, this OOC is legally considered to be a detention centre at the border, which means that the unaccompanied child is not considered to have formally entered the territory yet. Within 15 calendar days, the Immigration Office has to find a durable solution for the child, which may include return after an asylum application has been refused. Otherwise access to the territory has to be formally granted.
Unaccompanied minors who are caught on the territory without residence permit are sometimes held in detention for the duration of their age assessment procedure. This can sometimes take more than a week before this is rectified. In 2019, 3 children whose age was tested during detention were considered 15 years old after the test and had thus wrongly been held in detention. In 2020, two minor boys were held in detention because of doubts about their declared age. Because the Belgian authorities did not want to carry out a bone test while the boys were in confinement for sanitary reasons (covid-19), it eventually took 22 days before they were officially declared minors and released from detention. This practice has in the meantime been adapted and in 2021, most minors have been released in 6 days after their arrival.
No other vulnerable categories of asylum seekers are excluded from detention by law. Besides the consideration of the minority of age, no other vulnerability assessment is made whatsoever before deciding on the detention of asylum seekers, especially at the border. In practice, the detention of vulnerable persons remains problematic.
Organisations visiting detention centres have reported the presence of pregnant women and persons with physical and mental health conditions in detention, who do not always have access to the necessary mental health assistance. In 2018 for example, Myria, the Federal Migration Centre, reported the detention of a woman who was 22 weeks pregnant. She was being detained with a view to conduct a Dublin transfer to Poland (a transfer that ultimately did not take place). 
In 2019 a report was published by several NGOs based on the testimonies of visitors. One case reported concerned an Eritrean man, with clear signs of torture on his body, who committed suicide before being sent back to Bulgaria. Another case concerned a person who committed self-harm while being detained. He was subsequently followed by a psychologist and released upon recognition of the refugee status.
 ECtHR, Kanagaratnam and Others v Belgium, Application No 15297/09, Judgment of 13 December 2011. The Court found a violation of Articles 3 and 5(1) ECHR due to the detention of a Sri Lankan asylum seeking (who was eventually recognised as a refugee) mother with three underage children for more than three months.
 ECtHR, Muskhadzhiyeva and Others v Belgium, Application No 41442/07, Judgment of 19 January 2010. The Court found a violation Articles 3 and 5(1) ECHR due to the administrative detention for one month of a Chechen woman and her four small children who had applied for asylum in Belgium while waiting to be expelled to Poland, the country through which they had travelled to Belgium.
 Arrêté royal du 22 juillet 2018 | Koninklijk besluit van 22 juli 2018
 Council of State, Decision No 244.190, 4 April 2019.
 Article 74/19 Aliens Act.
 Article 40 Reception Act.
 On the technicality of this legal fiction, see inter alia Council of State, Decisions No 102.722, 21 January 2002 and No 57831, 25 January 1996.
 Figures confirmed by the Immigration Office in January 2020.
 Myria, ‘Myriadoc 8: Retour, détention et éloignement’, December 2018, available in French at: https://bit.ly/2FPAo6t, 45.
 Caritas, Ciré, JRS Belgium, Platforme Mineurs en Exil, Point d’appui and Vluchtelingenwerk Vlaanderen, Vulnerabilité et Détention en Centres Fermés, October 2019, available in French at : https://bit.ly/2Guh7ps.