Child migrants and asylum seekers are unnecessarily held in squalid immigration facilities and police lock-ups due to their immigration status or that of their parents.
The 67-page report, 'Two Years with No Moon: Immigration Detention of Children in Thailand,' details how Thailand's use of immigration detention violates children's rights, risks their health and wellbeing, and imperils their development.
The Thai government should stop detaining children on immigration grounds, Human Rights Watch said.
''Migrant children detained in Thailand are suffering needlessly in filthy, overcrowded cells without adequate nutrition, education, or exercise space,'' said Alice Farmer, children's rights researcher at Human Rights Watch and author of the report. ''Detention lockup is no place for migrant children.''
Human Rights Watch interviewed 41 migrant children and 64 adults who had been detained, arrested, or otherwise affected by interactions with police and immigration officials.
In addition, Human Rights Watch interviewed representatives of international and nongovernmental organisations, migrant community leaders and lawyers.
Immigration detention practices in Thailand violate the rights of both adults and children, Human Rights Watch said.
Migrants are often detained indefinitely, and they lack reliable mechanisms to appeal their deprivation of liberty.
Indefinite detention without recourse to judicial review amounts to arbitrary detention, which is prohibited under international law.
Prolonged detention deprives children of the capacity to grow and thrive mentally and physically. Yanaal L., a migrant detained with his family in Bangkok's immigration detention center for six months, told Human Rights Watch: ''My [five-year-old] nephew asked, 'How long will I stay?'
''He asked, 'Will I live the rest of my life here?' I didn't know what to say.''
The International Organisation for Migration reports that there are approximately 375,000 migrant children in Thailand, including children of migrant workers from neighboring countries, and children who are refugees and seeking asylum.
The largest group of child refugees living in Thailand are from Burma, many of whom fled with their families from Burmese army attacks in ethnic minority areas, and from sectarian violence against Rohingya Muslims in Arakan [Rakhine] State. Other refugees are from Pakistan, Sri Lanka, Somalia, Syria and elsewhere.
Migrants from the neighboring countries of Burma, Cambodia, and Laos tend to spend a few days or weeks in detention after they are arrested and then are taken to the border to be formally deported or otherwise released.
However, refugee families from non-contiguous countries face the choice of remaining locked up indefinitely with their children, waiting for months or years for the slim chance of resettlement in a third country, or paying for their return to their own country, where they fear persecution.
They are left to languish indefinitely in what effectively amounts to debtors' prison.
Immigration detention conditions in Thailand imperil children's physical health, Human Rights Watch found. The children rarely get the nutrition or exercise they need.
Parents described having to pay exorbitant prices for supplemental food smuggled from the outside to try to provide for their children's nutritional needs. Immigration detention also harms children's mental health by exacerbating previous traumas and contributing to lasting depression and anxiety.
By failing to provide adequate nutrition and opportunities for exercise and play, Thai immigration authorities are violating fundamental rights enumerated in the Convention on the Rights of the Child, which Thailand has ratified.
Children in immigration detention in Thailand are routinely held with unrelated adults in violation of international law.
They are regularly exposed to violence, and can get caught up in fights between detainees, use of force by guards, and sometime get physically hurt.
Severe overcrowding is a chronic problem in many of Thailand's immigration detention centers.
Children are crammed into packed cells, with poor ventilation and limited or no access to space for recreation.
Human Rights Watch interviewed several children who described being confined in cells so crowded they had to sleep sitting up.
Even where children have room to lie down, they routinely reported sleeping on tile or wood floors, without mattresses or blankets, surrounded by strange adults.
''The worst part was that you were trapped and stuck,'' said Cindy Y., a migrant child held from ages 9 to 12. ''I would look outside and see people walking around the neighborhood, and I would hope that would be me.''
None of the children Human Rights Watch interviewed received formal education while in detention, even those held for many months.
By denying migrant or asylum-seeking children adequate education, Thai immigration authorities are depriving children of social and intellectual development.
The Convention on the Rights of the Child says that all children have the right to education without discrimination on the basis of nationality or migrant status.
Under Thai law, all migrants with irregular immigration status, even children, can be arrested and detained.
In 2013, the United Nations Committee on the Rights of the Child, the body of independent experts charged with interpreting the Convention on the Rights of the Child, has directed governments to ''expeditiously and completely cease the detention of children on the basis of their immigration status,'' asserting that such detention is never in the child's best interest.
''Amid the current human rights crisis in Thailand, it is easy to ignore the plight of migrant children,'' Farmer said. ''But Thai authorities need to address this problem because it won't just disappear on its own.''
Besides ending the detention of migrant children, Thailand should immediately adopt alternatives to detention that are being used effectively in other countries, such as open reception centers and conditional release programs.
Such programs are cheaper than detention, respect children's rights, and protect their future, Human Rights Watch said.
In an August 14, 2014 response to a letter from Human Rights Watch sending out findings and recommendations, the Thai Ministry of Foreign Affairs denied that the detention of migrants was carried out in an arbitrary manner, and stated: ''Detention of some small number of migrant children in Thailand is not a result of the Government's policies but rather the preference of their migrant parents themselves (family unity) and the logistical difficulties.''
The government's seven-page response is included in the report's annex.
Thailand faces numerous migration challenges posed by its location and relative prosperity, and is entitled to control its borders, Human Rights Watch said.
But it should do so in a way that upholds basic human rights, including the right to freedom from arbitrary detention, the right to family unity, and international minimum standards for conditions of detention.
''Thailand's immigration detention policies make a mockery of government claims to protect children precisely because they put children at unnecessary risk,'' Farmer said.
''The sad thing is it's been known for years that these poor detention conditions fall far short of international standards but the Thai government has done little or nothing to address them.''
'Two Years with No Moon: Immigration Detention of Children in Thailand' is available at: