There is no federal law that stipulates that children and parents be separated at the border, no matter how families entered the United States.

Claims that the “law to separate families” was passed in 1997, those claims originated with a February 2018 Department of Homeland Security statement referencing “[l]egal loopholes [that] are exploited by minors, family units, and human smugglers.” The DHS statement claimed existing immigration policies “create a pull factor that invites more illegal immigration and encourages parents to pay and entrust their children to criminal organizations.”

However, neither the 1997 Flores settlement nor a 2008 human trafficking law cited in that release in any way stipulated that the government separate children from their parents:
A White House spokesman referred [Factcheck.org] to a DHS statement regarding a 1997 legal settlement and 2008 antitrafficking law affecting minors who are apprehended without a parent present:
Under the 1997 settlement, DHS could detain unaccompanied children captured at the border for only 20 days before releasing them to foster families, shelters or sponsors, pending resolution of their immigration cases. The settlement was later expanded through other court rulings to include both unaccompanied and accompanied children.
The William Wilberforce Trafficking Victims Protection Reauthorization Act of 2008 requires unaccompanied minors from countries other than Mexico and Canada to be placed in the care of the Office of Refugee Resettlement, or relatives in the U.S., while they go through removal proceedings. The bipartisan bill was approved by unanimous consent and signed by Bush.
But neither the court settlement nor the 2008 law require the Trump administration to “break up families.”A cluster of rumors about the controversial separation of families at the border held that the policy came before the Trump administration, either stemming from a 1997 “law” or purported policies of previous administrations. Those claims were false. No federal law required or suggested the family separation policy announced by Attorney General Sessions in several sets of remarks during April and May 2018.
An increase in child detainees separated from parents stemmed directly from a change in enforcement policy repeatedly announced by Sessions in April and May 2018, under which adults (with or without children) are criminally prosecuted for attempting to enter the United States:
The “zero-tolerance” policy he announced [in May 2018] sees adults who try to cross the border, many planning to seek asylum, being placed in custody and facing criminal prosecution for illegal entry.
As a result, hundreds of minors are now being housed in detention centres, and kept away from their parents.
Over a recent six-week period, nearly 2,000 children were separated from their parents after illegally crossing the border, figures released on [15 June 2018].
[Attorney General] Sessions said those entering the US irregularly would be criminally prosecuted, a change to a long-standing policy of charging most of those crossing for the first time with a misdemeanour offence.News items about Sessions’ comments on border policy often included a statement he made at a gathering for the Association of State Criminal Investigative Agencies in Arizona on 7 May 2018:
So, if you cross the border unlawfully, even a first offense, we’re going to prosecute you….
If you’re smuggling a child, we’re going to prosecute you, and that child will be separated from you, probably, as required by law. If you don’t want your child to be separated, then don’t bring them across the border illegally.In other articles, Sessions was quoted as saying on the same date:
If you are smuggling a child, then we will prosecute you and that child will be separated from you as required by law … If you don’t like that, then don’t smuggle children over our border.
[…]
We don’t want to separate families, but we don’t want families to enter the border illegally[.] We urge them not to do so.On 5 June 2018, CBS News covered an interview Sessions provided to radio host Hugh Hewitt. During the broadcast, Hewitt asked Sessions if it was “absolutely necessary… to separate parents from children when they are detained or apprehended at the border.” Several responses from Sessions were included in the article:
If people don’t want to be separated from their children, they should not bring them with them. We’ve got to get this message out. You’re not given immunity. You have to, you will be prosecuted if you bring, if you come illegally. And if you bring children, you’ll still be prosecuted.
[…]
[T]he United States can’t be a total guarantor that every parent who comes to the country unlawfully with a child is guaranteed that they won’t be, is guaranteed that they will be able to have their hand on that child the entire time. That’s just not the way it works … I don’t think it’s a moral right, Hugh. … If you come to the country, you should come through, first, through the port of entry and make a claim of asylum if you think you have a legitimate asylum claim. You shouldn’t try to get across the border at some desert site, some remote site unlawfully and expect not to be promptly deported. We’ve caught, over the years, millions of people, and they’ve been promptly deported. They don’t get trial in federal court.

Sessions did not make the statement attributed to him, but he did make a series of remarks in early April 2018 about a new border initiative involving the separation of children from parents at border crossings:
If you are smuggling a child, then we will prosecute you and that child will be separated from you as required by law … If you don’t like that, then don’t smuggle children over our border.
[…]
We don’t want to separate families, but we don’t want families to enter the border illegally[.] We urge them not to do so.On 7 May 2018, CNN reported that until April 2018, immigration officials used discretion to handle families or unaccompanied minors entering the United States without documentation:
It has long been a misdemeanor federal offense to be caught illegally entering the US, punishable by up to six months in prison, but the administration has not always referred everyone caught for prosecution. Those apprehended were swiftly put into immigration proceedings and, unless they met the threshold to pursue a valid asylum claim, can be quickly deported from the country.
The current DHS plan makes no special arrangements for those who claim asylum when apprehended. While they will be allowed to pursue their claims and could eventually be found to have a legitimate right to live in the US, they could still already have a conviction for illegal entry.On 7 May 2018, CNN reported that until April 2018, immigration officials used discretion to handle families or unaccompanied minors entering the United States without documentation:
It has long been a misdemeanor federal offense to be caught illegally entering the US, punishable by up to six months in prison, but the administration has not always referred everyone caught for prosecution. Those apprehended were swiftly put into immigration proceedings and, unless they met the threshold to pursue a valid asylum claim, can be quickly deported from the country.
The current DHS plan makes no special arrangements for those who claim asylum when apprehended. While they will be allowed to pursue their claims and could eventually be found to have a legitimate right to live in the US, they could still already have a conviction for illegal entry.

sources:https://www.snopes.com/fact-check/did-ag-say-if-inflict-fear-pain-children/
https://www.snopes.com/fact-check/was-law-separate-families-passed-1997/

Over the past few decades, the number of imprisoned parents in the U.S. has skyrocketed. From 1991 to 2007, it jumped by more than 357,000. Today, more than half of the 2.2 million people in the nation’s prisons and jails are parents of minor children.  Between 2006 and 2016, tens of thousands of children were placed into foster care solely because a parent was incarcerated. For about 5,000 of these children, their parent's rights were eventually terminated.  No significant racial disparities were found in the relative rates at which these parents’ rights are terminated. But given that African-Americans are disproportionately incarcerated — 1 in 10 black children have a parent behind bars, compared with about 1 in 60 white youth — this phenomenon impacts them in outsized numbers.

Mothers and fathers who have a child placed in foster care because they are incarcerated — but who have not been accused of child abuse, neglect, endangerment, or even drug or alcohol use — are more likely to have their parental rights terminated than those who physically or sexually assault their kids. 

When a someone goes to prison, nearly 65 percent of families are suddenly unable to pay for basic needs such as food and housing, the report found. About 70 percent of those families are caring for children under the age of 18. Women like Smith are often responsible for court-related costs associated with the conviction, and many families go into debt to pay those fees, leaving even less for food and shelter. When that family member gets out of jail, their loved ones are left with the task of supporting their reentry. This burden is ongoing since people with a criminal record often are unable to find work upon their release.

 “Poverty, in particular, perpetuates the cycle of incarceration, while incarceration itself leads to greater poverty,” according to “Who pays? The True cost of Incarceration on Families (Ella Baker Center for Human Rights).


In about 1 in 8 of these cases, incarcerated parents lose their parental rights, regardless of the seriousness of their offenses, according to the analysis of records maintained by the U.S. Department of Health and Human Services between 2006 and 2016. That rate has held steady over time. Female prisoners, whose children are five times more likely than those of male inmates to end up in foster care, have their rights taken away most often.
Since 2010, a handful of states including New York, Washington and Illinois have passed legislation to help mothers and fathers in prison keep their children. And in the coming months, Rep. Gwen Moore (D-Wisc.) plans to introduce in Congress an “incarcerated parents’ bill of rights,” which she said in an interview would make sure that most imprisoned parents who maintain a role in their kids’ lives do not have their rights terminated.

Read more: HOW INCARCERATED PARENTS ARE LOSING THEIR CHILDREN FOREVER
Who Pays? The True Cost of Incarceration on Families

Immigrants are Less Likely to be Criminals Than the Native-BornHigher Immigration is Associated with Lower Crime Rates

• Between 1990 and 2013, the foreign-born share of the U.S. population grew from 7.9 percent to 13.1 percent and the number of unauthorized immigrants more than tripled from 3.5 million to 11.2 million.
• During the same period, FBI data indicate that the violent crime rate declined 48 percent—which included falling rates of aggravated assault, robbery, rape, and murder. Likewise, the property crime rate fell 41 percent, including declining rates of motor vehicle theft, larceny/robbery, and burglary. 

Immigrants are Less Likely than the Native-Born to Be Behind Bars 

• According to an original analysis of data from the 2010 American Community Survey (ACS) conducted by the authors of this report, roughly 1.6 percent of immigrant males age 18-39 are incarcerated, compared to 3.3 percent of the native-born. This disparity in incarceration rates has existed for decades, as evidenced by data from the 1980, 1990, and 2000 decennial censuses. In each of those years, the incarceration rates of the native-born were anywhere from two to five times higher than that of immigrants.
• The 2010 Census data reveals that incarceration rates among the young, less-educated Mexican, Salvadoran, and Guatemalan men who make up the bulk of the unauthorized population are significantly lower than the incarceration rate among native-born young men without a high-school diploma. In 2010, less-educated native-born men age 18-39 had an incarceration rate of 10.7 percent—more than triple the 2.8 percent rate among foreign-born Mexican men, and five times greater than the 1.7 percent rate among foreign-born Salvadoran and Guatemalan men.

Immigrants are Less Likely Than the Native-Born to Engage in Criminal Behavior 

• A variety of different studies using different methodologies have found that immigrants are less likely than the native-born to engage in either violent or nonviolent “antisocial” behaviors; that immigrants are less likely than the native-born to be repeat offenders among “high risk” adolescents; and that immigrant youth who were students in U.S. middle and high schools in the mid-1990s and are now young adults have among the lowest delinquency rates of all young people. 
  
• SOURCE:http://immigrationpolicy.org/sites/default/files/research/the_criminalization_of_immigration_in_the_united_states.pdf