Anyone can speculate, but nobody will be accurate except the Judge who has ultimate power of sentencing. Usually, crimes like these result in a deferral program that teaches them not to do it again and if they do what they're supposed to do, the case gets dismissed after a period of time.
Speak to a good local attorney about it before going to court.
If the probation department contacts you, cooperate fully with them. They will be trying to get background information on your son. It is possible that he could get a deferred prosecution - which means that they will not prosecute him as long as he does what they require of him which generally includes a class, community supervision, reporting, possibly urine tests for drugs.
The case is a misdemeanor so even if he does not get the deferred from the probation department, he may be able to get it when he goes to court. You will be required to hire him a lawyer if you are not indigent. The lawyer can advocate for him.