you are speaking in a fictional "we" .. the wealthiest economies are built on pure selfish action, and grew like ivy in the garden in the last 500 years of expansion. Meanwhile, plenty of other cultures teach their children to compete with others based on language, "tribal" affiliation, other reasons.. You are trying to explain half of a world-view, and your ten year old easily finds the dissonance in that.

source: a person raised in the fictional "we" whose neighbors were not