See if you can get access to the room a week or more in advance to practice. If not, see if you can get more detail about the inside of the room, e.g. dimensions, ceiling height, color of walls and ceiling, etc. Then collect all the advice you can find, write it down as a series of options, and practice, test, practice, test. Recruit your son or someone else to be your practice model. There is no substitute for practice in comparable circumstances.
Also, see if you can get your son to wear a tie or stuff a hanky in his pocket that's 18% gray so you can do color correction later.
But seriously, a pure white hanky visible in the scene could give you a base for color balance. Alternately: before or after the ceremony find an opportunity to sneak up to the presentation position and get a shot of a gray card under the same lighting.
Don't wait, start planning and practicing now.