You can ask the judge (call his or her chambers) to inquire into the situation, but if you are going to be yourself called as a witness (especially for the defendant), then it is likely the case that you cannot be in the courtroom--they don't want a witness to see/hear other witnesses testimony, since he/she may change his/her testimony in response to it. You should be able to have a non-witness family member (e.g. an uncle, aunt, grand-parent, etc.) in the courtroom when you son is testifying, and you should be able to wait out in the hallway.