The purpose of this paper focuses on mothers' beliefs about their child's personality and development (stability or change and causal attributions) and how these beliefs can be affected by mothers' experience (being a mother of a six or of a twelve-year-old child and being a mother of a normally-developing or of a mentally disabled child). The scales were completed by several samples of mothers. The effect of the temporal orientation (retrospective or perspective) was also considered. The results show that the mothers rate their child with an optimistic bias while the mothers of disabled children are less positive than those of the broad-ranging sample. The results are also in accordance with the decrease of positiveness as the child grows. Finally, the optimistic bias differs in function of the temporal orientation for the mothers of normally-developing children and for the mothers of mentally disabled children. The retrospective change is also overestimated with regard to the prospective one in the broad-ranging sample. (Contains 2 figures, 10 tables, and 1 note.)