Gretel may have been a member if she still lived in Berlin. When they move, there are no other families around. Bruno even remarks,
" The new house, howeer, stood all on its own in an empty, desolate place and thre were no other houses anywhere to be seen, which meant there would be no other famillies around and no other boys to play with, neither friends or trouble." (pg 11- chapter two)
Later he says that the house is
"The middle of nowhere." (pg 13- chapter two)
So there is no one to form an organization with Gretel.
Gretel is thirteen, but both she and Bruno are sheltered by their mother and grandmother. Bruno doesn't even know what a Jew is,(pg 182, chapter-15) and Gretel knows that they should not have any contact with them, but it is INFERRED that she gets her information from Lieutenent Kohler, who she admires, after moving to Auschwitz and not her family. At Auschwitz, she is beginning to become politically aware. She has thrown away all her dolls and put up maps of Europe that she got from her father. She reads the newspaper daily and puts pins in her maps. If she had her friends around her in a big city like Berlin, she probably would have become a member.
Grandmother is especially strong about how she does not like the Nazi's. She says,
"The people you have to dinner in this house. Why it makes me sick. And to see you in that uniform makes me want to tear the eyes from my head." (pg 93 - chapter 8)
thankyou so much:) this helps a lot:D