Environmental or Physical problems that may be causing behavior

child upset by loud noise

Sometimes before setting up a whole behavior plan to deal with sudden increase in behaviors of a child you should check to see if there is anything in the child's environment or physical body that might be affecting them.
For example if suddenly they are really having alot of behavior problems you might check and see if they are sick or have an ear infection. That's sometimes a cause but the child can't or won't tell you how they feel, or they don't know what's going on with them.

Here are things to consider:

Noises (loud, strange, etc may bother kids)
Lights (too bright, hum loudly like ones in grocery stores/commercial buildings)
Need to use the bathroom (especially number 2....)
Too Cold/Hot