Alicia Farmer, a children's rights analyst at Human Rights Watch, said children from the Rohingya community in Myanmar need a safe haven after fleeing violence targeting their minority group.
"Yet Thailand locks up many who reach its shores, leaving them vulnerable to [human] trafficking and further abuse," she said in a statement Monday.
The rights group said more than 2,000 members of the Rohingya community arrived in Thailand last year. The country lacks the laws allowing Rohingya to register for asylum, however, and they don't have protection as refugees under international law.
Human Rights Watch said members of the Rohingya community in Thailand have left immigration detention centers for camps in southern Thailand. There, they're exposed to human traffickers.
The United Nations last year estimated 140,000 people, mostly from the minority Muslim community, were displaced because of violence in Rakhine, a coastal state in Myanmar.