The black backpack

Last weekend, I bought my daughter a used black backpack from the animal thrift store.  It was kind of dirty but  for only $3.00 it was a good deal.  It also has wheels for the days when the books are particularly heavy.  When my son, Nathan, saw the backpack he said, "That is a man's backpack."  When this didn't get much of a response from me he tried another approach, "I am in middle school and Gabriel is only in 5th grade so I am the one that needs the backpack."  When again this failed to give him the desired result, he got grouchy and took it out on Gabriel.  I am not sure what he did because I was not in the room when it happened but Gabriel told me,  "I hate Nathan."  I have noticed when I say "No" to him he takes it out on his sister.  I will need to talk to him about that.  I never thought a  backpack could be such a big deal.