They may be included as explanations 1 and 3 on Bryan's list, but maybe: A) Children aren't aware of the benefits of trade (cooperation). Most things they have are provided from their parent(s), and so they don't see much benefit to cooperating with others.
B) Children know that trade gets them something, but their gain from trade are not are great as adults. Children might not have much to offer each other. Cooperating with another kid might get you another friend, but cooperating with another adult might get you a job or other tangible benefit. This could help explain why kids might disrespect other kids, but might be polite in front of adults (in addition to being taught "manners"). Jason
