Theexwife
It's a tricky one, you do not want people at school saying anything however I can understand the parents would be annoyed that you have become involved.
They know that he smells and maybe they nag him to shower and use deodorant, they may feel it is a reflection on them that he doesn’t wash properly.
The majority of teenage boys go through a disgusting stage.
It is a reflection on them if their son does not wash properly, you know.
And his school-mates will make remarks, at least the girls will!
Age 11, he probably does not want to listen to his parents, and might be more willing to listen to his gran!