I have a couple of tips, you will want to be in a ground blind so you are not seen drawing the bow. If you hit the turkey, make sure it is the neck, spine, or head. I had a friend hit a turkey with his bow in the chest. The turkey was able to fly away and my friend said we never found the arrow. A week later, he was bow hunting for deer and saw the turkey walking around with the arrow stuck in it. He then finished off the turkey.
Sounds like a real treat for your son (and you). I am also going this weekend, but still havn't tried my bow. I give you credit for that. Did you see the Guilitoine Video in the Turkey Hunting Group area? Looks like those nice wide bladed broadheads are the trick, something that within 2-3 inches of the neck lops that puppy right off. Hopefully that wont scar the young lad ;)
I'm going to try it with a regular brawd head. I looked into it and those guillotine heads require a larger, heavier arrow. This causes it to drop real quick, so close shots are your only option. From what I've seen, as long as hit him below the wing socket, I should have a good chance at downing a tom.