My son (12) drinks a boost high protein shake each morning with his toast and fruit. he is complaining of nausea afterward. could it be the boost?

Maybe,maybe not: Any physical symptom could arise from an exposure to these products. Try skipping a few days & see if it quits happening & restart it. If it is an issue it will likely return when it is introduced again.

Boost not for kids: Boost is not designed for growing children who are healthy and need to instead eat a well balanced diet of food. Boost can cause nausea. It is pretty sweet. Eat foods with complex carbohydrates, some protein and low fat for breakfast. Boost is for adults who have a low appetite and won't eat enough. Growing boys need real food.