Illegal migrants are being prosecuted, incarcerated until their criminal case may be addressed fully, while they are being identified, records researched, and their family status determined, as to any minors caught crossing the border with the adult.
First time lawbreakers face criminal Misdemeanor punishment when found guilty.
An adult who previously was caught crossing our border is subject to criminal Felony changes for their offense, and incarcerated until their case is adjudicated, and may face whatever remaining jail time remains pending from their initial crime, prior to being processed and removed, or deported, or prior to the criminal alien fleeing prosecution in the first case.
Incarcerated criminal aliens are removed from society, and any confirmed minor relatives who were caught with them during the crime may be detained, likely by HHS, until their status is fully determined.
Aliens who enter the U.S. without a Visa, and declare themselves Refugees seeking Asylum in the United States, will be detained, and minor family with them when they so declare will be detained by CBP, keeping the family together once the adult/child relationship is confirmed, and the adult identity and criminial history, if any, is determined.
Minor Aliens who's parents seek Asylum may be detained with the parent(s) for up to 20 days, under US Law. When the adult Asylum seeker will be held for longer than the law allows for minors, said minors will be separated from the family and detained separately by CBP, or HHS, whatever is deemed to be legal and appropriate, as they await the determination of the parent's status.
No entitlement to U.S. Residency is offered or assured for any illegal migrant, be they adult or minor.
So, one can see that we have several entities at play, depending upon the criminal status of the adult alien, and the time being detained to determine identity, criminal history, and outstanding adjudication matters when applicable for said adult aliens.
Family detention is limited to 20 days, and the amount of time necessary to vet and identify any alien, then to determine Asylum status in cases where the aliens so request such status, is very likely to grossly exceed legal detention of said minors by CBP in a family unit.
Minors, those claiming to be minors and family, need identification, vetting and criminal history review, including gang affiliations and criminal history in the home country prior to, and during detention and subsequent incarceration, and meanwhile, without criminal history, such minors are housed, fed, given medical care, English language instruction, and general education, as well as supervised recreation.
I saw a headline a few days back noting over 13 Million minor U.S. Citizens endure a lower living environment when compared to incarcerated/detained alien minors in U.S. custody.