Right after Benjamin declares that by coming to know God, they would know what is just and true, he begins to describe what being just and true would mean in their own lives. Specifically, he is interested in how the people of Zarahemla would treat each other. Once again, we remember the conditions preceding this speech. The severe internal contention was a recent reminder of how the community should not treat others in that community.
Perhaps it is in that light that we note Benjamin suggesting that parents should not suffer their children to fight and quarrel one with another. Note that right after that comes the declaration that neither should they suffer their children to serve the devil, or the evil spirit. Benjamin had noted that their contentions had come from their listening to obey the evil spirit in Mosiah 2:32 and 37. Thus, it seems that Benjamin is not counseling that children should not quarrel in the way that children in families might, but is concerned with the kinds of contentions that had recently divided the community.