Child collision detection?? help please

If you have multiple colliders on a Gameobject they behave as "merge" into one collider, as in: You can not differentiate between the different colliders inside OnCollisionEnter(). You need to make a separate child object for each collision zone. To differentiate between the different zones you have different functionality inside the OnCollisionEnter() of the child game objects.

Note: Unless each child has it's own rigidbody, where you lock rotation and position to "disable it" as much as possible, the OnCollisionEnter() inside the parent will also be triggered with each collision. The OnCollisionEnter() event will essentially move up the hirachy until it reaches a game object with a rigidbody component.