instantiated gameObject set parent code example
Example 1: how to instantiate as child unity
Instantiate(obj, pos, rot, parent);
Example 2: unity instantiate as child
//SetParent() method
//https://docs.unity3d.com/ScriptReference/Transform.SetParent.html
//or something like this
var myNewSmoke = Instantiate (poisonSmoke, Vector3(transform.position.x,transform.position.y, transform.position.z) , Quaternion.identity);
myNewSmoke.transform.parent = gameObject.transform;