Answer:
Eyes.
Step-by-step explanation:
In a portrait, eyes play a vital role in revealing the behavior of the subject in the frame. Eyes, as referred to a window of a soul, is true in portrait also. A painter once stated that the most important feature in any portrait is the eyes as they create a passage to the viewers to know that the painter had formed a relationship with the object.
So, even in a portrait of a child, the most important feature to be focused on will be eyes. Thus, the correct answer is the eyes.