The correct asnwer is the following:
Child a is a young adolescent. Child b is around 6 years old. Child c is around 4 years old.
This is because psychology studies and explains how the development of children and young people happens, and the transformations our mind goes through as we age. A young adolescent is capable of understanding that people may have ambivalent feelings, while when we turn 6 years old, we start to understand that people's behaviors do not necessarily reflect their thoughts and feelings. Lastly when a child is around 4 years old, he/she would believe that when a person sits quietly, they are not thinking much, because that is how developed a child's mind is by that age.