AMNA NAWAZ: Last night, we brought you the story of Ukrainian mothers and grandmothers going to Crimea to rescue their children, some of the nearly 20,000 who have been forcibly deported to Russia or Russian-controlled parts of Ukraine.

Tonight, with the support of the Pulitzer Center, filmmakers Amanda Bailly and Anton Shtuka and special correspondent Jane Ferguson show us how reunion can be both joyous and difficult.

JANE FERGUSON: For these women, the return to Ukrainian soil is everything, the first time they can really believe it, that they got their children back.

NATHALYA, Ukrainian Mother (through translator): I'm exhausted, but happy that I'm finally in my homeland, in Ukraine.

I'm happy that I'm here with my child.

That's the most important thing.

Everything else is little things in life.

We just need to get home to see our cows and pigs.

(LAUGHTER) JANE FERGUSON: They have crossed over from Belarus after a journey of some 3,000 miles to get their children back from Russian-controlled areas of Ukraine.

NATHALYA (through translator): They had a lot of questions.

For example, whom do you visit there?

My son.

Why do you want to go visit him?

It's my son.

JANE FERGUSON: They are just some of what Ukraine says are as many as 19,000 families have been separated when the Russian military and Ukrainian collaborators working at the children's schools moved their children to Russian-occupied areas, saying it was for their safekeeping, and never returning them.

Another boy, Sasha, is rushed into a quiet car.

He has autism and is nonverbal.

After six months away from his family, he is struggling with physical touch and night terrors, his mother tells us.

Almost all men are not permitted to leave the country because of the war effort.

It fell on these women, many who had rarely left their hometowns before, to go on a dangerous journey to get them back.

That journey was long, fraught, and secret.

But as their best pulled into Kyiv, they were met by a throng of international press.

While they were traveling into Russian-controlled territory, the International Criminal Court announced that Russia's deportation of their children was a war crime, and issued an arrest warrant for President Vladimir Putin and children's rights commissioner Maria Lvova-Belova.

She herself took custody of a Ukrainian teenager from Mariupol last year.

Journalists Amanda Bailly and Anton Shtuka chronicled the women's journey, and returned to visit them and the children after the initial media frenzy died down.

Svetlana, now back in Kherson after retrieving her granddaughter, remembers a harrowing journey, where she had to be careful what she told Russian border officials about her visits true meaning.

SVETLANA, Ukrainian Grandmother (through translator): They started questioning me about where I was going and why.

They took phone numbers and said: "Look, if we call these phone numbers, if this information is not true, you are going to suffer very, very badly."

I said: "I am not lying to you.

I am telling you the truth."

So they let me go.

I was frightened, almost crying.

JANE FERGUSON: Svetlana's granddaughter, Nastya, is finally home in Kherson in Southern Ukraine, liberated from Russian control last fall.

Nastya was taken to summer campgrounds inside Russian-controlled territory.

The camps, seen here in promotional videos, were used before the war as holiday spots for children.

After the full-scale invasion in 2022, Russian authorities started transferring Ukrainian children there from territories they had seized, telling parents they were being taken to protect them from the fighting.

Some, like Nastya's grandmother, initially gave permission for them to go for two weeks.

But they were never returned.

Those working there were, according to the children interviewed here, pro-Russian Ukrainians and encouraged Russian propaganda amongst them.

Svetlana says Nastya was not physically harmed, but her experiences at the Russian camp frightened her.

Nastya's wider family now find her changed, distant.

SVETLANA (through translator): She doesn't trust people.

Even the other kids noticed.

"Why don't you talk to us," they ask?

"No, you give all your attention to your animals, to your dog."

She spends a lot of time with dogs.

She just wants to be alone day after day.

JANE FERGUSON: Nastya remembered only being texted by a schoolteacher who was collaborating with the Russians, persuading the children to move to Crimea.

NASTYA, Ukrainian Student (through translator): I received a Telegram a message on my phone from a cool chat, like, let this opportunity in Crimea.

My homeroom teacher sent the text message.

JANE FERGUSON: Once they had crossed over, the teacher left them there and fled to Russia, she said.

It would be six months before her grandmother rescued her from the camp.

Nastya may be home, but that home is still in Ukraine, along the front, and dangerous.

Shelling gets close, and the interview must be moved inside.

Her grandmother's journey to bring Nastya home came just in time.

The camp management were planning to move the children out before the busy summer season of paying guests.

The children were under increasing danger of being moved into Russia, made Russian citizens, and put up for adoption.

NASTYA (through translator): The camp management told us we would be taken under custody on April 7 if we were not taken away by our families.

They would give us citizenship and a passport, just like this, or just send us to different camps.

They could take us to Moscow, to St. Petersburg.

JANE FERGUSON: Like Svetlana, Nathalya was interrogated by Russian border officials as she went to retrieve her fifteen year old son, Artem.

Lawyers for the local charity Save Ukraine had prepped her.

NATHALYA (through translator): I had to tell the truth, that I was going to visit my child.

I gave the address of the school in Perevalsk and Artem's phone number.

They asked how he got there.

I told him they were evacuated because there was shelling there.

I did the best that I could.

JANE FERGUSON: Artem remembers the day collaborators at his school handed him over to Russians.

ARTEM, Ukrainian Student (through translator): We didn't want to go, but we found out we were being evacuated.

Everyone started to panic.

Then the soldiers came, put us in the military truck, and took us away.

The little ones cried.

They were scared.

But it was too late.

JANE FERGUSON: It was a month before a teacher gave him a phone to call his mother, he said.

At the boarding school he was taken to in the occupied region of Luhansk, he described being indoctrinated with Russian propaganda.

ARTEM (through translator): They explained to us that Russia is good and Ukraine is bad.

They said that Russia restores everything, but Ukraine only destroys everything.

JANE FERGUSON: Some of the teenagers had much darker experiences.

Nina, who is 16 years old, was forced to do military training.

Pictured here in a black ski mask, she said she was trained to use a gun.

NINA, Ukrainian Student (through translator): We had competitions mostly on Sunday and Saturday.

There were three teams, and your teams competed to dismantle machine guns, look for mines and lob grenades.

JANE FERGUSON: For Nina's mother, Alina, her reunion, after she too traveled into Russian-controlled areas to get her back, was all the more emotional.

ALINA, Ukrainian Mother (through translator): Little by little, she told me everything, even showed photos of where they were with guns, swarming up ropes and shooting.

They had a physical exam, blood tests.

I have all the documents.

I think they were being prepared for something, since she had the complete health screening, ultrasounds.

All her organs were screened.

JANE FERGUSON: Nina struggled more than most when she got home.

Her mother moved away from their front-line home with her,got her a comfort dog, and continues to try to help her heal.

In the front-line city of Kherson, teenager Masha remembers the day she was deported to Russian-controlled Crimea.

MASHA, Ukrainian Soldier (through translator): There were a lot of buses.

Maybe 15 buses.

And it was three days, maybe even four.

The buses were taken to different places.

I went to the same camp as my friends, to Mechta.

JANE FERGUSON: For the kids, being at camp was, at first, a great novelty, said Masha, a fun time away from home.

They were fed, entertained and occasionally had school classes.

MASHA (through translator): After a month, we were thinking, why are we still here?

Some kids wanted to go home.

We started asking questions like, why aren't we going home?

Someone said: "It's not safe to go there yet.

It wasn't clear."

They said: "You don't understand.

It's not safe there, and your parents can come to pick you up any time."

Then, we were told that Kherson would become part of Russia again, and then they would take us home.

JANE FERGUSON: Those like Masha's mother had initially agreed to have their children go to holiday camps in Russian-controlled Crimea.

Living under Russian occupation, they were told the children would be sheltered from the fighting and would be returned in two weeks.

In the end, the children did not return.

JANNA, Ukrainian Mother (through translator): Of course, if I had known, I would never have let her go at all.

She is just a young teenager, and I am responsible for her.

Of course, I blame myself, not the child, not my husband or anyone else.

MAN: We made the decision together.

JANNA (through translator): Yes, but I sent her there.

MAN: I knew that Kherson would be left like this, that the probability of street fighting was very high.

And we could see, it was clear that they were preparing for this, putting fortifications and sandbags everywhere.

Street fighting is, of course, scary.

Everyone saw what Mariupol was like, how people died there.

And of course, this is why we made the decision.

If we only knew.

JANNA (through translator): Well, when it reached nearly six months, I had already torn my hair out.

I hadn't slept.

I had sleepless nights, was on pills.

JANE FERGUSON: Masha said she was moved to another camp.

There, volunteers came to retrieve some of the younger kids, but Masha and others were told to stay inside.

MASHA (through translator): After a month, we were thinking, why are we still here?

Some kids wanted to go home.

We started asking questions like, why aren't we going home?

Someone said: "It's not safe to go there yet.

It wasn't clear."

They said: "You don't understand.

It's not safe there, and your parents can come to pick you up any time."

Then, we were told that Kherson would become part of Russia again, and then they would take us home.

JANE FERGUSON: After some time, she says, the camp staff began hinting at Russian adoption projects.

MASHA (through translator): They said that: "Well, there is a law in Russia that children can't live without parents for six months.

So if you are not picked up before this date, they will simply take custody of you."

JANE FERGUSON: While legal wranglings play out far away from the front lines of the war, these families return to surviving the war that rages around them.

Svetlana may have Nastya back, but the constant shelling outside reminds her that life with her remains dangerous.

SVETLANA (through translator): Every day is like this, all day from morning until late, or even all night.

So, we're used to it.

I won't leave and don't want to.

It is all in Gods hands.

If we should die, then we will die in our homes.

And if fate continues to have us live, survive and raise children, we will continue to live like this.

JANE FERGUSON: A long-awaited spring counteroffensive by Ukrainian forces has begun.

Areas like Kherson and Kupiansk, home to many of these families, could become even more deadly.

NATHALYA (through translator): Our biggest wish is to wake up one day and find out that we won.

We want it to be quiet here again.

We want families not being separated.

JANE FERGUSON: With each Russian shell that lands by their homes, these Ukrainian families, now finally reunited, are reminded that their lives together, while precious, remain fragile in the face of this war.

For the "PBS NewsHour," I'm Jane Ferguson.