Previous studies have found discrepancies between parent and child reports of parental favoritism. Some studies have also found that these discrepancies have unique effects on children’s psychosocial adjustment. Nonetheless, much is still unknown about discrepancies between parent-reports and child-reports of parental favoritism and how they are associated with children’s development. The current study examines discrepancies in multi-informant reports on parental favoritism in relation to children’s internalizing and externalizing problems. The sample consisted of 556 mother–child dyads and 554 father–child dyads (46% boys, Mage = 12.52 years, SDage = 1.18). Polynomial regression analyses and response surface analyses were used to disentangle the effects of parent–child discrepancies in perceived parental favoritism. The results indicate that children reported higher parental favoritism than their parents. And the highest internalizing and externalizing problems occurred when both the mother and the child reported high maternal favoritism, and when both the father and the child report high paternal favoritism. Therefore, these findings partly support the assumptions based on the operations triad model. The findings also highlight the importance of the discrepancy between child- and parent-reports on parental favoritism in the development of children’s internalizing and externalizing problems.