I've saw another version of this story with a few more details, and the kids apparently where using the drawings to threaten the kid they drew. But arresting them is still terribly excessive.
If the kids that drew the pictures where using them to threaten somebody then they should be suspended for a week or so, assuming this is the first problem. If the pictures where just jokes or some idle time wasting then a week of after school suspensions seems more in order to me.
Sadly, given the horrible over reactions of schools when I went, this doesn't surprise me in the least. Schools are unwilling to address any but the worse problems. And when they do have to face up to a problem, they over react. Indiscriminantly expelling students and bringing in police and other stuff.
Jay