ISTANBUL -- In a textile factory in Istanbul, workers toil over sewing machines. But look closely, because the workers are children.

Filming with a hidden camera, we found scores of factories using child labor in Turkey. Most, perhaps all, of the children are from Syria.

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Some told us they were as young as 11 -- refugees from a war now easily exploited.

A Turkish worker on the minimum wage earns around $450 a month. A Syrian child, working 12 hours a day, earns as little as $160.

At a school for Syrian children in Istanbul, the boys -- aged 10 to 12 -- are just beginning to learn to read and write, because until recently most of them were full time workers.

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The school's founder, Shafik Suleyman, told us he offers free tuition to encourage parents to send their children back to class. But sometimes that's not enough.

Some parents aren't earning enough money to feed their families. "No, they have to -- they're being forced to send their kids to work," said Suleyman. "They've got no choice."

Leyla Akca is a psychologist who treats Syrian child refugees and their families, and told us many factories prefer to hire children over their parents.

"You can overwork the children and they're not going to be oppositional, they're not going to ask for their rights. They don't know their rights. So they're just going to work like slaves and it's easier to keep them as slaves than doing it to an adult."

Turkey has taken in around 3 million Syrian refugees, spending billions of dollars to shelter and feed them. While they're safe there, there's very little stable work, and not much hope of building a future.

That's why so many Syrians have risked their lives in rickety boats to reach Europe. But now the European Union has promised Turkey nearly $7 billion in return for its help stopping the refugees.

The crackdown has worked. For Syrians, the door to Europe has slammed shut.

But the factories that prey on them appear to be operating with impunity, and hundreds of thousands of Syrian children in Turkey are growing up illiterate and powerless to change their fate.