Marcia Biggs:

Mosul may be liberated from ISIS, but the fear on its streets is palpable. As some of its almost one million citizens begin to return home, the issue on everyone's mind is the possibility of a resurgent ISIS.

Throughout the nine-month battle, Kurdish and Iraqi officials tried to root out ISIS fighters and sympathizers, screening and detaining thousands from the mass of people who fled the city. Many of those detained were children, and some were what ISIS called their Cubs of the Caliphate, seen here in this propaganda footage.

ISIS made the recruitment of children for military purposes routine, sending children as young as 4 years old to training camps, where they would learn to fight, kill, and even die for the Islamic State.