my son is 6 and keeps getting cramps on the arch of his feet, almost like charlie horses, they last 5-20 minutes. I took him to a doctor one time for it but at that moment he he wasn't having one. his doctor said make sure he drinks enough, which he does. he doesn't eat junk except once in a great while he might have one sweet snack, mainly he eats fruits and healthy snacks
It may be worth it to see if he could use an arch support or some kind of insert in his shoes depending on if he has high arches or flat feet. Either one can cause foot cramping.