Increasingly, scholars are exploring the politics of migration and the shifting terrain of citizenship from a critical mobilities perspective. To contribute to these discussions, in this paper, I explore how processes of sub-citizenship occur as nation-states craft immigration, citizenship, and border securitization policies and practices. I argue that complex and shifting processes of sub-citizenship largely occur through the nation-state’s production of ‘insiders’ (‘citizens’) and ‘outsiders’ (‘non-citizens’). As a nascent attempt to introduce sub-citizenship, I draw upon recent high-profile cases of family separation, abuse, and neglect experienced by children with ‘illegal migrant’ status in the United States and Australia. Under the international nation-state system and the neoliberal globalization paradigm, the border policing powers of nation-states are primed to expand and intensify processes of sub-citizenship. Those at lower levels of the sub-citizen hierarchy are at risk of experiencing various forms of state-led violence, including deportation, detention, and torture.