Apply Material to Specific Children

Hello, so I am implementing a power up type of system. I have a material that is just a red color that I want to apply to specific body parts of the player. Specifically these:

In my Awake method I try to get access to the render with this code:

     void Awake() {
         CharacterController = GetComponent<CharacterController>();
         SpotCollider = GetComponent<Collider>();
         SpotRender = GetComponent<MeshRenderer>();
     }

After this on onTriggerEnter I want to change those components to a red material. I'm not sure how to pick and choose children.

Thanks for your time.