Answer :
She isn't sure she wants to see the children because something about the way Bruno said "they're out there" made her feel nervous. Hopes this helps!! :)
Before Gretel looks out Bruno's window in Chapter 4, she hesitates. She is not sure that she wants to look out, because she is unsure she will like what she sees. Gretel is worried that she might see something that will frighten her or confuse her. When she finally looks out, she does not understand what she is looking at. She ventures the theory that the camp is a farm, although she realizes she is most likely wrong. In the end, she is unable to come up with a satisfactory explanation.