This is an interesting statement to think about in regard to this novel, because I personally don't think that fear is actually a dominant theme. Certainly there is an element of fear in the way that the group of telepaths fear discovery, but it is not a controlling fear that dominates them and overpowers them. On the contrary, it is a realistic threat that the telepaths themselves seem more than capable of dealing with. Note the first step that the group took at Uncle Axel's suggestion to make sure that they told nobody about their "gift" and how it affected them:
Furthermore, in trying to convey Uncle Axel's seriousness to them I must have stirred up an uneasiness that was in all their minds, for there was no dissent. They made the promise willingly; eagerly, in fact, as though it was a burden they were relieved to share. It was our first act as a group; it made us a group by its formal admission of our responsibilities towards one another. It changed our lives by marking our first step in corporate self-preservation, though we understood little of that at the time.
I am not trying to downplay the fear of the children or the very real threat that faced them, but at the same time the group themselves, through their unity and togetherness, seem more than capable of overcoming their fear by working together and sharing. If you are not convinced by my reasoning, consider the number of times that fear is mentioned and compare it to the number of times that the strength of the group is refered to in overcoming that fear.