CNN  — 

Protests along the US-Mexico border heated up again Monday as thousands of undocumented migrant children remained separated from their parents.

One of the main protests is taking place in the Texas border city of Tornillo, the site of a temporary shelter for unaccompanied migrant children.

Another protest is happening outside the US Border Patrol Central Processing Center in McAllen, Texas. There, demonstrators held signs such as “Parents Everywhere Care” and “Free Them.”

Protesters gathered Monday to denounce the separation of migrant children and their parents.

After widespread criticism over family separations caused by President Donald Trump’s “zero tolerance” policy, Trump reversed course last week by signing an executive order aimed at keeping some families together at the border.

But it did little to calm the outrage. And on Sunday, Trump called for the deportation of people without judicial proceedings to thwart what he referred to as an invasion by “these people.”

More than 2,000 children who have been separated from their families still await reunions with their parents. The Department of Homeland Security released a plan for putting back together the thousands of families on Saturday night, but it appears the reunions won’t happen quickly.

On Sunday, celebrities including Lena Dunham, Sia and Amber Heard joined protests in the border city of Tornillo, the site of a US-Mexico border checkpoint and a temporary shelter for unaccompanied migrant minors.

Other cities along the border have also been the site of protests. Chanting protesters in McAllen briefly blocked a bus leaving a migrant detention center as they yelled “set the children free” and “shame on you” at Border Patrol officers on Saturday.

Demonstrator Martha Mercado tried to stop a bus with immigrant children outside a Border Patrol processing center in McAllen, Texas.

Massachusetts Democratic Sen. Elizabeth Warren visited the center in McAllen on Sunday. “It’s a disturbing picture,” she said after her visit.

“They’re all on concrete floors in cages.”

After days of confusion, the Trump administration released its plan for reuniting children still in the custody of Health and Human Services over the weekend.

Under the plan, children will be kept in custody and returned to family members only after the parents’ deportation proceedings are completed. The families will be reunited before they are deported, or if the parent is released from detention, after the parent applies to serve as the child’s sponsor.

Parents are being offered the option to sign voluntary departure orders to speed up their cases and are told they’ll be reunited with their kids before they are deported if they do – a move that has raised questions from lawyers who represent undocumented immigrants.

CNN’s Faith Karimi, Eric Levenson, Tal Kopan, Eli Watkins, Holly Yan, Meg Wagner and Brian Ries contributed to this report.