(lol at the above)
Hi Island Mom, the age of 11 is grand! I'd suggest taking your son to Fidos for dinner. You'd have live entertainment everywhere and kids as well as adults love entertainment!
There is music, tourists, locals, LOTS of charactors comin and goin... depending on the night all kinds of action can be happening, not bad food and a great island ambiance. This would be my first choice to recommend to any tourists with age differences.
We dine at many other places, but I do think this would be a good match for you and your son 1st time on Island.
Enjoy Ambergris Caye!