AMNA NAWAZ: Apprehensions of migrants at the U.S. southern border reached a record high at the end of last year.

But before crossing into the U.S., many in this increasingly global group travel more than 1,500 miles through Mexico.

With producers Sam Weber and Christine Romo, we recently went to Mexico's southern border with Guatemala to report on this desperate journey.

When we met them on this Chiapas, Mexico, roadside, these families, originally from Venezuela, had already been walking for 15 days.

Where are they heading now?

JASON, Venezuelan Migrant (through translator): We are going to the United States, God permitting.

AMNA NAWAZ: Why did you leave?

DIANA, Venezuelan Migrant (through translator): My country.

My country.

The government is horrible.

Under a blazing sun in near 90-degree heat, they share that they are heading to the U.S. to seek asylum.

We ask what they need.

Water, water.

MAN (through translator): Food for the children.

AMNA NAWAZ: Ten-year-old Brittany has already witnessed and lived what no child should.

BRITTANY, Venezuelan Migrant (through translator): We had to pass through the jungle and cross rivers.

They stole our money and lied to us.

AMNA NAWAZ: When's the last time she had any food or water?

BRITTANY (through translator): I don't know.

AMNA NAWAZ: But she's fueled by a simple dream.

BRITTANY (through translator): I want to study.

AMNA NAWAZ: Study?

What do you want to study?

BRITTANY (through translator): Doctor.

Little brother Jason is just five.

JASON, Venezuelan Migrant (through translator): I'm going to the Disney castle.

AMNA NAWAZ: You're going to the Disney castle.

And with that, they press on, each step they hope bringing them closer to a better life.

As migration worldwide erupts to record levels, this part of Southern Mexico has become a global crossroads, with thousands of asylum seekers passing through each day, most on their way to the United States.

ELI CRUZ, U.N. International Organization for Migration: We are here right now, and here is mainly where the people enter through Mexico.

AMNA NAWAZ: Eli Cruz leads the Tapachula suboffice for the United Nations International Organization for Migration.

ELI CRUZ: It's not just that women or men are traveling by themselves.

They're traveling with their families.

There are a lot of children.

We are seeing a lot of different profiles with a lot of vulnerabilities.

AMNA NAWAZ: For years, migrants crossing through Mexico were largely from Central America.

2023 marked the first year that people from South America outpaced them, with record numbers from Venezuela and Ecuador, according to Mexican government data.

But the patterns continue to shift.

What about people from even further away?

For example, at the U.S. southern border, some of the biggest jumps we have been seeing over the last three years have been for people from Russia, from India, from China.

Have you been seeing that here as well?

ELI CRUZ: Yes.

In the last years, we have been seeing a lot of these nationality, also people from Afghanistan or from Bangladesh.

AMNA NAWAZ: Over the past decade, Mexico has become an increasingly popular and accessible route to the U.S. for Asian and African migrants.

In fact, out of the 195 recognized countries in the world, Mexican officials say 120 nationalities have come across their southern border.

The majority of those crossings happen here.

This shallow stretch of Suchiate River is all that separates Guatemala from Mexico at this point and rafts regularly ferry people across.

But in some ways, the most difficult part of the journey is still ahead, some 1,500 miles and many more obstacles before the U.S. southern border.

But those who can afford it skip all those obstacles and gain swift passage to the northern border.

Smugglers like Mario handle all the details.

MARIO, Smuggler (through translator): My clients all want to arrive safe and sound in the United States.

AMNA NAWAZ: We're using a different name to protect him from cartel retribution.

He charges up to $21,000 per person for longer journeys and says his network has moved 50,000 people into the U.S. since 2021.

What do you tell them when they approach you?

Do you guarantee them that they will be able to make it?

MARIO (through translator): It's my word and my reputation the line.

Out of all the clients that I have had, only two or three have been detained.

The rest are in the United States.

AMNA NAWAZ: "NewsHour" has no way to verify that claim.

I ask him about migrant stories of abuse and assault on their journeys.

MARIO (through translator): Yes, it's true.

The people that happens to don't have the money to pay for my services.

The overland trip across Mexico can take around 15 days, but I can move any nationality into the United States via plane in a matter of hours.

There is always a way to get in.

AMNA NAWAZ: With scarce resources, 24-year-old Rosa and her family are making their own way to the U.S.

They left Venezuela in September of 2023, traversing the deadly and dangerous Darien Gap into Central America.

ROSA, Venezuelan Migrant (through translator): We saw horrible things, dead women, children, and we worried constantly about what could happen to our children, if the river would take them, if they would dehydrate, if they would suffer from malnutrition because we didn't have enough food, or if they would need medication.

AMNA NAWAZ: Thirty-two-year-old Merlin, a former government official, says she fled political persecution.

She and the other mothers banded together to get their families to the United States.

MERLIN, Venezuelan Migrant (through translator): Some brought tents.

Some brought medicine.

We organized everything.

We are a total of 16 people, five mothers, all traveling together with our children, and we share everything, and we help each other along the way.

ROSA (through translator): Sometimes, we would run out of everything and have to go without food and water.

If all we had was a piece of bread, then we made sure all of the children ate, so they could survive, because they are not as strong as we are.

AMNA NAWAZ: In Mexico, they have entered a so-called containment zone set up by Mexican officials under U.S. pressure.

Checkpoints pepper the roads.

Migrants without paperwork can be detained.

Even those who make it to Mexico's north can be bussed or flown back to the south, an effort to alleviate pressure at the U.S.-Mexico border.

Near the riverbank, families wait to board a bus provided by Mexican immigration.

There's no shared schedule, timing, or final destination.

U.S. officials tell "NewsHour" this unpredictable effort aims to move migrants from dense cities into less populated areas and keeps them in Southern Mexico.

But that hasn't stopped the flow of migrants.

There are no official government numbers, but some officials and NGOs estimate between 4,000 and 6,000 migrants arrive daily.

Roughly half are processed by Mexico's Refugee Agency known as COMAR.

The other half are entering under the radar and not registering.

"NewsHour"'s repeated requests for an interview with a COMAR official were denied, citing election season restrictions.

Merlin says they know Mexico would be the toughest part of the journey, but they're not deterred.

MERLIN (through translator): We are heading out now.

We have high hopes and we're excited to move ahead in our journey.

We don't know where they're taking us, but we're going to stay positive.

AMNA NAWAZ: After several days walking and busing through Mexico, Rosa, Merlin and family arrive in Mexico City more than six months after they first left Venezuela.

From here, they plan to try and get an appointment with U.S. immigration through the CBP One app, a legal route for asylum seekers, before continuing on to the border.

It's at this point in the journey that countless families get close, only to get stuck.

You haven't been able to get an appointment yet.

How long have you been trying?

JUAN, Mexican Migrant (through translator): No, we have been trying for an appointment every single day.

AMNA NAWAZ: Juan and Rocio have spent nearly two months at this shelter along the U.S.-Mexico border with their five kids.

Cartel violence in their home state of Guerrero has paralyzed a once-thriving state.

When you think about your life ahead, if you make it into the United States, what do you want for your children?

What does that better life look like?

ROCIO, Mexican Migrant (through translator): I want my children to do well, to go to school and be someone in life.

I don't want them to live in fear.

Susana Hurtado Rochin is a program coordinator for Save the Children in the state of Sonora, on the border with Arizona.

For many of the children who come through here, the journeys that they have made are just unimaginable.

What's the impact of that kind of journey on a child?

What does it do to them?

SUSANA HURTADO ROCHIN, Save the Children (through translator): Both adults and children arrive with mixed emotions.

They arrive with an idea of getting to the border and crossing right away into the United States.

And then they get here and they're stuck and they're conflicted about being so close, but yet so far away at the same time.

AMNA NAWAZ: Save the Children works directly in shelters across the U.S.-Mexico border, setting up child-friendly safe spaces.

SUSANA HURTADO ROCHIN (through translator): The goal is to give them a sensation of taking back control of their lives and not living in standby mode, so that they can continue with their lives, meet people, make friends, and do it all in a place where they feel safe to express their feelings and speak about their emotions.

AMNA NAWAZ: Seven-year-old Carely and her sister, 11-year-old Citlalli, are already preparing for life in the U.S. CARELY, Mexican Migrant (through translator): I just know one thing in English.

You're my baby.

AMNA NAWAZ: You're my baby?

Oh.

(LAUGHTER) AMNA NAWAZ: They tell us they prefer life in the shelter to life back home.

What do you like about being here?

What's it like staying here?

CARELY (through translator): I like the games.

AMNA NAWAZ: Oh, the games?

CARELY (through translator): What I like best is being with my family.

AMNA NAWAZ: Their parents, Juan and Rocio, say they will wait as long as it takes to get an appointment and enter the U.S. legally.

The border crossing is just a few miles away, but, for this family, close enough is good enough for now.

We will have a second report tomorrow from the U.S.-Mexico border in Arizona on what asylum seekers face when they cross the border and how U.S. immigration officials are coping with it all.