What will happen if he received a summons to appear in court for trespass to dwelling (unenclosed curtilage to dwelling) 810.09(1) (A)2 (1 M)?

My son was charged in November 2012 with possession of marijuana under 20 grams, contributing to the delinquency of a minor (his 17 year old brother) &possession of drug paraphernalia. He has gone to court, is in the process of his probation, has done his court appointed narcotics anonymous class & he is going to do his 15 hours of community service. This charge is the same day but was not on his original citation or his probable cause affidavit. Can you please explain what can happen to him and why we weren't aware of this earlier? Thanks for any help.