Cousins of opposite Gender Playing Together
Question

                Are cousins of the opposite sex allowed to play together?
Praise be to Allah.If the cousins are male and female and are young and
    have not reached the age where they could feel desire and temptation, then there is no
    harm in their playing together. If they are older, then it is forbidden because cousins
    are not Mahrams (close relatives whom one is permanently forbidden to marry and with whom
    the rules of hijaab and segregation are relaxed). Cousins are ‘Ajaanib or strangers
    (non-Mahrams) to the daughters of their paternal uncles (father’s brothers) and
    maternal uncles (mother’s brothers). And Allaah knows best.