Auto-Scrolling Level - crushing player results in death

I've started learning how to use Unity this summer and for my first game I wanted to make one level of a top-down shoot 'em up. I've managed to code the camera to automatically move while the player moves along with it (I did this by making the player a child object of the main camera). I have also created a boundary for the player by creating child GameObjects that have box colliders around the camera. However, I'm stuck figuring out how to kill the player if the player collides with the the camera boundary and an enemy / obstacle (crushing the player).

If someone knows a solution please let me know.