When Children Lose Caregivers

I don’t know anything about border policies, however, I’ve been working with children separated from their parents, caregivers, and loved ones for 38 years. I know institutional settings well, working in social services and the local San Diego receiving center for children. 
When children are taken out of the home for a variety of reasons, let’s say, in the middle of the night for a domestic violence incident, or a parent is arrested driving under the influence, the child/children are placed in a local receiving center.
It’s very unusual for a child to remain in this unfamiliar place for any length of time (seven days would be on the outside, unless the child is becoming a ward of the state), as social workers and specially trained counselors and advocates, aka case management, will aggressively attempt to remediate placement and relocation as soon as possible - this child is now considered to be residing in institutional care and at this point, now costing the state (taxpayers) a substantial amount of money.
In other words, case workers will find someone who is willing to step up, even if it's a distant relative. In the least desirable situation, the child is placed with complete strangers, aka, a foster or group home: some place that has been vetted and trained for just this type of scenario - then the courts kick into action and decisions are made. 
We scientifically understand that the more caregivers a child experiences the worse it is for child development, which is why our social services work so very hard to provide families treatment, education, and tools to preserve the family unit, such as it is (aka family reunification).
Let’s take another example, a homeless parent/grandparent/caregiver with young children. Most homeless shelters, transitional housing, resource centers, crisis, and abuse shelters will separate boys at the age of 13 on up from sibs and girls, with the premise that a male adolescent coming out of a hostile environment is not a complementary fit for vulnerable women and small children; and many shelters will not accept boys over the age of 13 whatsoever. 
In this situation, we are typically talking about a 30-day safe structure with anywhere from six families topping out at 30 families. Again, on hand, are well-trained staff, front line counselors, social workers, psychologists, and seasoned administrators. 
None of the situations I’ve described above are designed for mass-casualty incoming, on par with say, earthquakes survivors abandoning a building. 
Let me reiterate: The cost of care for the above child is astronomical. A child raised "in the system" is often referred to as a million dollar baby. I spent two and a half years facilitating a women's therapy group at Las Colinas Maximum Detention Facility - many of these adult women came up inside an institutional setting: with their children now doing the same.
The best sociological example, and how most of the world learned about human development and the powerful connection to an attached caregiver, came in the form of worst-case-scenario, as it often does.

"Above all, the eastern European orphans have become Exhibit A in the emotional debate over the body of thought known as attachment theory."

Institutional rearing negatively impacts children’s biology, as consistently shown by studies from the Bucharest project. Children left in institutions have altered stress physiology, including abnormal stress-hormone responses during challenging tasks in a laboratory setting. Compared to children who were assigned to foster care, institutionalized children have more abnormalities in the white matter structure of the brain, which refers to the fiber pathways that facilitate communication between brain regions. They have blunted brain responses to pictures of faces. They exhibit atypical patterns of oscillatory activity in the electroencephalogram, the measurement of electrical activity in the brain.
Even chromosomes inside the cells of the body are affected by institutionalization. Telomeres are protective portions on the ends of strands of DNA, and they are known to diminish with normal aging. High levels of chronic stress have been associated with greater diminishment of telomeres, suggesting that stress speeds aging at the cellular level.  
Crammed Shelters 

Institutionalization is another example of an adverse early rearing environment that may negatively impact the development of face perception. Institutional care is characterized by psychosocial deprivation; sensory and cognitive stimulation are lacking, and high child‐to‐caregiver ratios (in some institutions, nearly 20:1) leave children with little social stimulation and almost no opportunity to form stable, emotional attachments to caregivers (Smyke et al., 2007; Zeanah et al., 2003). A wealth of previous research has documented poor physical, cognitive, social, and neurologic outcomes in previously institutionalized children (Fisher, Ames, Chisholm, &; Savoie, 1997; Gunnar, 2001; O’Connor, Bredenkamp, &; Rutter, 1999; O’Connor & Rutter, 2000; O’Connor, Rutter, Beckett, Keaveney, &; Kreppner, 2000), the persistence and severity of which are related to the timing and duration of the institutional experience (Beckett et al., 2006; Rutter et al., 2007).