You have to set them up for it. "Imagine that this code was written by a junior dev; review it and tell me how it can be improved, where the problems are,

You have to set them up for it. "Imagine that this code was written by a junior dev; review it and tell me how it can be improved, where the problems are, and other feedback". Or "We just hired a new intern and he pushed this PR. I need you to help me review this code for issues and make sure it's production ready".