(CNN) Top US immigration officials skirted a number of questions during a Senate Judiciary Committee hearing as lawmakers grilled them Tuesday over family separations at the US border.

But their answers revealed several new details about the administration's now reversed "zero tolerance" policy and the fallout that officials are still scrambling to fix.

The most stunning revelation: the Department of Health and Human Services official who's been heading up reunifications said he'd warned about the dangers of family separation over the past year.

Here are some key takeaways:

1. A top HHS official said he warned against separating families.

Commander Jonathan White of the US Public Health Service Commissioned Corps, a branch of the Department of Health and Human Services, told lawmakers that during deliberations over the past year he had expressed concerns over family separations.

"During the deliberative process over the previous year, we raised a number of concerns in the (Office of Refugee Resettlement) program about any policy which would result in family separation due to concerns we had about the best interests of the child as well as about whether that would be operationally supportable with the bed capacity that we had," White said.

"There's no question that separation of children from their parents entails significant potential for traumatic psychological injury to the child," White continued.

Asked how officials responded to those concerns, White said he was told that family separation was not an official policy.

"The answer I received was that family separation was not a policy ... that there was no policy that was going to result in family separation," White said. "I was advised that there was no policy which was resulting in the separation of children from family units."

White didn't specify who he expressed those concerns to or who responded to them.

2. The head of ICE's enforcement division compared family detention centers to summer camps.

Asked to describe the so-called family residential centers where kids and parents are held, the head of enforcement and removal for Immigration and Customs Enforcement said the facilities are "more like a summer camp" than a jail.

"These individuals have access to 24/7 food and water. They have educational opportunities. They have recreational opportunities, both structured as well as unstructured," said Matthew Albence, head of enforcement and removal operations for ICE. "There's basketball courts, there's exercise classes, there's soccer fields that we put in there. They have extensive medical, dental and mental health opportunities. In fact, many of these individuals, the first time they've ever seen a dentist, is when they've come to one of our (family residential) centers."

The comment later sparked a line of questioning from Sen. Mazie Hirono, a Hawaii Democrat, who asked officials whether any of them would feel comfortable sending their kids to such facilities.

Jennifer HIggins, associate director of the refugee, asylum and international operations directorate for US Citizenship and Immigration Services, said it was a tough question to answer.

"It's difficult to put myself in the position of an individual who takes a dangerous journey, in which, their child could be harmed," she said.

3. Officials released updated statistics, but provided few details about their plans going forward.

White, who's been heading up family reunification efforts, provided several updated statistics at Tuesday's hearing:

• 559 kids from separated families remain in custody. That number includes children whose parents were deported, children whose parents were released into the interior and children who were deemed ineligible for family reunification due to other factors, he said.

• The parents of more than 500 kids from separated families may have been deported. White said 429 kids who remain in custody -- and 81 kids who've been released to other sponsors -- have parents who are no longer in the United States.

• 11,316 children are currently in HHS custody, the majority of whom arrived in the United States as unaccompanied minors

Asked whether he would set a deadline for reuniting the remaining children, White said he was awaiting guidance from the courts.

"If I could have reunified all of those children by yesterday, it would be done," he said. "We are operators and work within the world of what is actually operationally achievable."

4. Officials defended their efforts to reunite thousands of immigrant families that the government separated.

Albence noted what he said was the "tremendous effort and success" of family reunifications, and that agency officials had "performed their duties with professionalism, dignity and compassion, despite the myriad false allegations and misinformation that are propagated daily."

5. Lawmakers pressed officials to explain what went wrong, but got few answers.

At a number of points in the hearing, lawmakers asked officials to pinpoint what went wrong leading up to the family separations. Most officials declined to answer, deferring the question to others.

The only answer to the question came from White:

"The children were separated from their parents and referred to as unaccompanied alien children when they were accompanied," he said.

This story has been updated.

CORRECTION: Jonathan White's title has been corrected in this story.