A knife is still considered a deadly weapon. It is apparent the State Attorneys Office (SAO) has elected to try your son as an adult.
Legal disclaimer: This answer is offered for informational purposes only. It is not offered as, and does not constitute, legal advice nor does it constitute an attorney-client relationship. Thank You
If you are unable to afford a private attorney he will have to cooperate with his Public Defender so they can defend him. Your son can get a very lenghty prison sentence so if you have any means to hire a private attorney I would recommend it.
I do not know much about the public defender's office in Orlando, but I will tell you this: there are some outstanding assistant public defenders in the state of Florida. Unfortunately, there are also some not so outstanding ones. The same is true of the private bar. The biggest difference between the average public defender and the average private attorney is that the average public defender has a much larger case load. This means less time to be spent on each individual client's case.
It also means that the fire that is burning now will get the most attention. Your son's case is relatively new and he is probably going to spend some time in jail while his attorney gets his case ready for trial.
If you cannot afford to hire a private attorney, it is important to be both vigilant and patient. Pay attention to what your son's attorney is doing and not doing. If you have concerns, tell the attorney. If he or she does not address your concerns, ask to speak to his or her supervisor. At the same time, you and your son must be patient. Your son is facing very serious charges that can carry a long prison sentence and the stigma of a felony conviction. His attorney has a lot of work to do and your son is ultimately going to need to trust his or her judgment to make the right decision in this case. Give the attorney the opportunity to do his job.
Regarding the charge title in the clerk records, know this: the clerk's records are not always accurate. There will be a charging document called an "information" filed by the state attorney's office against your son (if that has not already happened). That document is the only document that really matters regarding what your son's charge is.
If there was no gun, and more importantly, no allegation of a gun, then your son will be charged with robbery with a deadly weapon. On the other hand, if the store clerk or other witness claims to have seen a gun, your son could be charged with Robbery with a Firearm. The state does not have to produce the gun to prove the allegation (although it certainly helps them if they have the gun).
Both charges are very serious, but the main difference is that being charged with Robbery with a Firearm places this case under the 10/20/Life statute. That law says that, if convicted, your son would face a mandatory minimum 10 years in prison for possession of the gun during the commission of the robbery, 20 years if the gun went off, and 25 to life if someone was injured. The most relevant here would be the 10 year mandatory. if convicted of robbery with a firearm, the 10 year sentence would be the minimum sentence your son could get and he would serve it day for day (no early release). He could still get more time. This 10/20/Life sentencing scheme is not an issue if he is only charged with Robbery with a Deadly weapon.
The good news is that whatever your son is charged with, he will likely be eligible to be sentenced as either a youthful offender (limiting the maximum time he could serve to 6 years in prison) or even as a juvenile (limiting his sentence to a juvenile program or juvenile probation). While he may be eligible, the judge would be under no obligation to impose such a sentence, but he or she would have the option.
And of course, your son might even have a chance to win his trial, if he chooses to go that route. His attorney should eventually be able to give you some idea of how likely that would be.
This will be a very difficult time for both you and your son, but do your best to stay positive and supportive.