Do you have one?
I do and he is my son. He is super skinny and very active. But when we go to the doctor's office she tells me he is heavy for his age and he has to lose weight. I pick up his shirt and proceed to give her a "wtf" look and ask WHERE. She takes one look at him and notices he is all muscle for an 8 year old. Then nods in agreement with me that he is perfectly fine.
This boy can eat! I have to buy a lot of food because he is constantly hungry. He snacks throughout the day on healthy things like fruit and vegetables. During a growth spurt I took him to an all you can eat restaurant and watched him polish off three full plates of food. This boy is playing football this year and the coach just smiled and said, "This boy is solid!" He isn't fat he is just solid.