I think it is normal. I substitute teach and on the very warm/hot days when the kids come back in from recess after running a while it is AWFUL in the room. Most of the teachers have a fan. We see this 3rd grade and up.
Just make sure he is clean and uses the deoderant.
I have to roll my windows down when certain friend of my daughter gets in the car with us because her feet are SO smelly. When she comes here, I always put her shoes in the garage.