For your son, I recommend getting him a high-quality protein powder that has whey or casein as the primary protein source. These two types of proteins are fast-acting and can be quickly digested by the body. They also contain all essential amino acids which are necessary for muscle growth and repair.

I would suggest getting him a flavored protein powder that he likes, but make sure it doesn’t have any unnecessary ingredients like added sugars or artificial sweeteners. It should just be pure whey or casein protein with some natural flavoring.

Another option is to make homemade protein shakes using fresh fruits and vegetables as the base. This way, he can get a variety of nutrients while still getting enough protein. You could also add some healthy fats like avocado or nuts for added energy and satiety.

Do you want me to provide any specific brands or recipes?