The present study addresses the issue of how the differences in age and roles with their parents can affect the children’s choice of the argumentative strategies they adopt in their discussions. The findings show that when children refer to a third person as a source of expert opinion, the expert always proves to be an adult, and not another child. Looking at this argumentative choice typically made by children, it is reasonable to assume that for them the reference to an opinion of an adult is a stronger argument than the reference to an opinion of another child. However, the actual effectiveness of the argument from adult-expert opinion depends on the extent to which the premises (endoxa) the argument is based on are shared by parents and children.