As a wave of unaccompanied children adds to the already large numbers of immigrants entering the United States, humanitarian groups warn that resources to serve the vulnerable population are running thin.

Fr. Sean Carroll of the Kino Border Initiative, a migration advocacy organization, was able to visit a federal facility housing migrants in Nogales, Ariz., but was not allowed to minister to the people there.

"They didn't offer any explanation," he said of the border authorities. "They said we are unable to receive volunteers and donations."

Fr. Carroll received a briefing by the Border Patrol and was able to tour the facility in Nogales.

"My overall impression was that their basic physical needs were being met," he said of the child migrants. "What's less clear to me is whether their spiritual, psychological and emotional needs are being met."

The priest said that he is "available and willing" to provide the sacraments to the child migrants, many of whom are Catholic, "but we're not being allowed to do that right now. That's the problem."

"I really see these children as refugees," he told CNA. "And they are. They're fleeing extreme violence and poverty, and many of their lives are at risk. And coming north is an act of sanity, I think."

"And the U.S. needs to treat them as such," he said. "And it's part of what it means, I think, to respect their God-given human dignity."

The number of unaccompanied child migrants to the U.S. has doubled in the past year, with many of the children fleeing violence in El Salvador, Guatemala and Honduras. The overwhelming numbers, combined with already high rates of immigrants, mean that needs are great and sometimes go unmet.

U.S. facilities along the Mexican border are "completely overcrowded" due to the recent surge in migrants, said Kim Burgo, the senior director of disaster services for Catholic Charities USA.

She added that the women and children crossing the border are "completely exhausted" and "in desperate need of compassion and care."

"The current Border Patrol facilities are filled," Burgo told CNA. She added that "those women and children are in desperate need of compassion and care" and that Catholic Charities is providing food, clothing, shelter, and in some cases counseling to the migrants.

"Families coming through, imagine their journey. They've been walking or traveling for the last, anywhere from seven to 21 days coming through," she said. "By the time they get here, they're completely exhausted. Their children many times are dehydrated, malnourished. And so we try to attend to those needs."

Brenda Riojas, a spokeswoman for the Diocese of Brownsville, Texas, told CNA that the migrants are not expecting handouts at the border, but sometimes their possessions have been confiscated by the authorities.

"They're tired, they're hungry. They are scared, confused," she said. "And so we are there to provide them a meal, provide them a change of clothing, provide them a little safe haven to kind of catch their breath and rest a bit and help them navigate their travel plans, for those who need some assistance before they continue on their journey."

Riojas said that one center for the migrants opened in McAllen, Texas, and served 200 on its first day. A second shelter opened in Brownsville, Texas. The shelters minister to 50 migrants on a slow day, but up to 200 on a busy day.

The shelters offer a rest stop for the migrants, who have been caught and processed by Border Patrol Agents. Riojas said that a medical center is available as well as showers provided by the city and cots for people to rest. The volunteers give them packets for their journey to meet up with family or friends in the U.S.

Fatigue and dehydration are the most common problems, she said, although more serious struggles are also being faced by those who have suffered greatly on their trip to the U.S. Catholic Charities has made counselors available to these individuals.  

Despite an outpouring of volunteer help and supplies, Riojas expressed concern that the centers could keep up with the current level of migrants. "I think right now what we're really concerned about is sustainability," she said. "Because there's no clear indication as to how long this will continue."

Volunteers are taxed, she added. "Once you go in, it's hard to even leave the center."

In El Paso, Texas, Melissa Lopez is providing for the legal needs of migrants who were able to give authorities a sufficient reason to stay in the U.S. Some of the eligible reasons include family members living in the U.S., applications for asylum, and fleeing domestic violence.

Lopez, who is the executive director of El Paso's Diocesan Migrant and Refugee Services, Inc., believes the number of applications for asylum will increase.

"I think unfortunately when they live in very, very violent countries – I think some of the countries in Central America have murder rates that rank near the top in the world, so that's the environment they're coming from – I think we're going to see an increase in asylum applications because many of them are scared."

Lopez said that current immigration laws can be unreasonable and restrictive.

"For a U.S. citizen who is applying for their sibling to obtain lawful status in the United States, 20 years just seems like an incredibly unreasonable amount of time," she said. "So I think that's just one example of how broken our system is."

"I have cases where I truly believe that if the judges or the immigration officials had a little more discretion, than the result of the case would have been different. But their hands are tied, there's only so many things that they can do."