Bruno is sheltered by his family. He lives in the midst of a death camp, but his mother and father keep him innocent of what happens on the other side of the fence. Shmuel is a different story. He also shelters Bruno. Shmuel hints at things and reveals what happened to his home and family but goes mo further. There are multitude of boys at the camp, but they are kept isolated. This would account for shmuels remaining innocence.
This is the most basic skill in science. Observations are made by using the 5 senses. Good observations are essential in learning the other science process skills.