Washington CNN  — 

The FBI and Department of Homeland Security sent a joint warning to law enforcement across the country about the concern over a growing trend of girls and boys wanting to fight with ISIS in the wake of the detention of a 17-year-old Northern Virginia teen last week, according to a law enforcement official who has read the report.

The source says law enforcement is tracking “lots of cases” like that around the country and they’re growing increasingly concerned about the issue. The warning was sent out over the weekend.

The warning lays out motivations for boys and girls. For boys: they tend to be older going over to fight and be a part of foreign fighters, or they want to attack in the U.S. (like the Brooklyn case). For girls: they tend to be younger and have a fanciful notion of what life is like in Syria. They often want to go over and be Islamic brides.

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