Its not just kids though, obviously. Any nieve drop out from society will do.
You may of seen some of the Islamic state individuals on the news, claiming Sharia law etc etc around London a few years back. Odd balls, each one. Pushed forward from the crowd to speak out, while the clerics sit in the back ground organising and cajoling them from under a "friendly" arm(or hook) . The body language and positioning in the group was painfull to watch, the staging was so blatant, yet the individuals completely oblivious.
Grooming exists in many forms. From the church to Isis. Savile and Glitter to (allegedly)the colour pink for Girls is said not to be a natural choice, but one society forces on them, for example.... ( Bollards to that last one btw) How wide is your range of acceptance of "training" ...?
Boris Johnson made some comments a few weeks ago that made him a better profiler than the orthoroties imo. Nail on head!
Putins reach much goes much further than we accept. As Syria would be very differant today if not for his stance on western intervention. Ok, waffling now.

Back on topic. If we allow the "drop outs" (for want of a better phrase) from society to free fall, one has to ask how low can they go and will you accept the consequences. Clearly there are no depths too low in some quarters.