minor in possession of alcohol

What is the name of your state? Georgia
my son was a passenger in a truck involved in a wreck. the driver is 16, my son and the other passenger are 17. the driver had bought some beer before picking up my son and it was in his truck. my son admitted that he knew it was in there and took a few sips earlier but they each blew 00 on the breathalizer. he was arrested and charged with possession of alcohol by a minor and has a court date in august. my questions are: what can we expect as punishment? do we need a lawyer? is the charge legal since he did not know the kid had the beer until later and he was not driving? we have done our parental part with our son, now i would simply appreciate some legal advice.

someone also told me he could use a first time offender plea. any information about this also would be appreciated.