Compound collider

I have a parent object, which has four children cubes. The parent has rigidbody, no collider. The four cubes only have colliders, which trigger tags are set true. I want to handle collision in the parent object. However, it didn’t work. I know use onCollisionEnter may work, but I must use trigger. Could anybody give me some ideas?

Thanks in advance.

Try OnTriggerEnter