I would suggest since your son doesn’t have any symptoms, that you do exactly as you mentioned. Cut out refined sugars, perhaps substitute with an occasional sugar free treat. Try to emphasize veggies and protein and use low carb guidelines for his food choices. I would use probiotics and colostrum (colostrum can’t hurt, but be careful not to go overboard on the probiotics). I would not try to put a child with no symptoms on a strict anti-candida diet, I think it might interfere with his growth, but I would modify the diet in minor ways to make it more liveable for a child. Do some research into recipes, and have some good snacks and meals from the diet available for him.
I believe my son also has candida with no symptoms except persistent bloat. We both have immune issues, and lymphocyte tests showed that he has no defences to candida albicans. I have a very bad infestation mmyself, so I do think he has some issues as well. Thaknfully, he has no symptoms. I try to encourage good food choices for him (he’s 17), and in doing so, he has developed a pretty good balanced diet Best of luck with your son. You approach sounds sensible and age appropriate.