Sphere Colliders on parent object and child object

I have a gameobject which hierarchy as ZombieGO > HeadGO, BodyGO, Armature. Now what i'm working on is to have sphere trigger colliders for attack range and sight range (large one is for sight range and small is for attack range),small one is attached on the main parent object and the big one attached on the BodyGO...

now i have attached scripts for trigger collider events to both ZombieGO(parent) and BodyGO(child), my parentGO is triggering right when the BodyGO triggers, i dont know why...could it be because i have attached them inversely of their hierarchy?

please help!!

Thank You.