Los Angeles — With big smiles and colorful backpacks, tens of thousands of students in the Los Angeles Unified School District walked into their first day of class Thursday. But heading into this new academic year, some families say they are living in fear.

Melissa, an undocumented mother of three U.S. citizen children, said her 8-year-old is afraid.

"When we hear that agents are nearby, we run or hide, and he's scared," Melissa told CBS News.

She says she has been forced to make a plan in case she is detained and deported.

"We've spoken to our eldest," Melissa said. "He'd be in charge of his siblings. It's sad to talk about these plans."

Immigration enforcement activity has picked up across the L.A. area over the past four months. In July , federal agents on horseback swar

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