Collision of child is detected as collision of parent with Rigidbody2D

I have an Enemy gameobject and AttackCollider gameobject. AttackCollider is parented to Enemy.

The Enemy gameobject has a Rigidbody2D component. But it has no collider. My collider is in AttackCollider.

Now when I detect collision with AttackCollider's collider, it detects colliding with Enemy. When I removed Enemy's Rigidbody2D component, it detects colliding with AttackCollider. Why is that? Can anyone explain?

 void OnCollisionEnter2D(Collision2D collision)
 {    
     // prints "Enemy" when Rigidbody2D is attached to Enemy
     // prints "AttackCollider" when Rigidbody2D is removed from Enemy
     Debug.Log(collision.gameObject.name);
 }