My son is 8 years old. He is taller and heavier than most of the other players. But he is not an assertive person by nature.
His Dad and I have explained to him that if he will listen to the coaches and do as they say he will be ok. We tell him that if he can learn to do this it will help him to be able to stand up to the kids that pick on him.
I just want him to keep trying and not to make up excuses to avoid it. I don't want to baby him, but I also don't want to ignore that he has a very real (and even valid) fear.