Republican lawmaker heckled over border crisis: 'What are you going to do for these babies?' "Tents and Walmarts?" a heckler yelled. "They're babies!"

As the immigration policy looms large in the national consciousness, border-state lawmakers are feeling the pressure from constituents who are outraged that children are being separated from their parents.

Under Trump's new "zero tolerance" immigration policy, the children of men and women caught crossing the border illegally are placed in government custody while their parents await prosecution in ICE detention centers.

Since the policy went into effect, more than 2,200 children have been isolated from their parents, and many are now housed in crowded shelters -- prompting fury from religious leaders, immigrant advocates, and child health specialists alike.

It was a 6-year-old girl at Republican Rep. Michael Burgess' town hall in Denton, Texas, who articulated constituents' anxiety Monday evening:

"Why does Donald Trump think it's OK to leave kids from their moms?” she asked.

His academic response -- citing two bills working their way through the House -- didn't seem to pacify his audience.

"Tents and WalMarts?" a heckler yelled, referencing one shelter facility made of soft-sided tents and another recently converted from a Walmart. "They're babies!"

"You're responsible for what happens here!" screamed another.

"You're protecting Trump!" accused a third, amid a chorus of boos.

Trump has said he hates to see children suffering under this "horrible" policy, which he claims is law.

It's not law. No law mandates separating families. It's a policy Trump announced in April that went into effect in May.

But the president has also suggested using family separation as a negotiating tool, refusing to reverse the policy unless Democrats agree to his other immigration reform priorities, like funding his "big, beautiful wall" at the southern border.

At his town hall, Burgess promised he'd work with Congress to reform the immigration system.

"I think this is a very good chance that something, in fact, may be done," he told the 6-year-old, noting it would likely be a "quite historic" week on "border security."

In a Twitter stream, the congressman clarified his views, arguing that "the Trump Administration is enforcing existing law -- a constitutional responsibility of the executive branch. ... The American government should not incentivize illegal immigration. In the interest of safety, we must not encourage sending kids through dangerous conditions in order to cross the border and gain entry."

But some citizens worried undocumented children are being used as pawns.

"Would you describe what's currently happening on the border as a healthy environment for those children?" one woman at the town hall asked.

"Well, no, of course you wouldn't," Burgess conceded, later adding, "when I have done these town halls previously, the sentiment has been, we want our laws on the border enforced."

"I haven't been sleeping because of what's going on," another woman said through tears at the town hall. "What are you going to do for these babies?"

"Engaging with constituents is a vital responsibility of the office," Burgess said in a statement to ABC. "This week, and always, I welcome and consider each constituent's input."

ABC News' Geneva Sands contributed to this report.