Sanitation is nonexistent, rats bite those who dare to fall asleep, and drinking water is inaccessible: These conditions and more are endured by thousands of migrant youth in Thailand’s squalid and overcrowded detention centres, according to a new report by Human Rights Watch.

Every year, Thailand submits thousands of migrant youths and refugee seekers, including Cambodians, to arbitrary detention in immigration facilities or police lock-ups due to their immigration status or that of their parents, the report finds. The majority of these children come from countries next door, such as Cambodia and Myanmar, and the experience is traumatising, contributing to lasting anxiety and depression, as well as stymieing their growth and development.

“The conditions are absolutely disgusting; you have toilets overflowing and children having to sleep sitting up because there are no beds at all,” said Alice Farmer, a child rights specialist and the report’s author. “There are clear UN standards on the minimum conditions for confinement, but, to be clear, Thailand is not even coming close to meeting those regulations.”

While hundreds of refugee children, including Khmer Krom, Hmong and Rohingya, are indefinitely detained for months or more, even larger numbers of children are cycled through the system in a couple of days or weeks, the report says.

At least 2,500 children from Cambodia, Myanmar and Laos pass through the largest detention centre in Bangkok each year before being repatriated.

The children, especially those who stay only briefly, are deprived of any formal education and often do not get nutrition or physical exercise imperative to their health. Parents reported that as the detention facilities often failed to provide adequate meals, they were forced to buy expensive black market food.

“Sometimes, they’d turn off the water for 15 to 18 hours,” said one detainee quoted in the report, while a 10-year-old Cambodian girl added that she was given, “just a little rice” during the length of her stay.

The children are kept in the same cramped cells as adult strangers in what Farmer called an “ad hoc arrangement that is violating international standards laws and leaving them vulnerable to abuse”.

In a seven-page response to the report, Thailand’s Ministry of Foreign Affairs said it was aware of some of the poor conditions in its detention centres, but added: “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.”

HRW is urging an end to the detainment, which the group says could be replaced by more humane alternatives like conditional release or family shelters.

“Hostile and violent detention centres are no place for children to grow up,” Farmer said.