Unruly

Unruly describes a mental state of not wanting to be obedient, and therefore being difficult to control.

It's a word that--no surprise here--is often used about children.  But it can also be used about a group, especially when that group becomes a mob.

Another curious feature of this word is that while there is the negative--unruly--there is no positive form--ruly.  In that sense, it's like yesterday's word--unkempt--which also exists only in the negative.

And yes, as you might expect, the word comes from Middle English, and is related to the verb meaning to rule.