If it is sudden onset it could be subconjuvtial hemorrhage due to the bursting of a small blood vessel, usually it dissappeared without any medical intervention. Other is conjunctivitis which is associated with eye discharge especially in the morning for which treatment is usually antibiotic drops to be applied in the eyes. In summary if child well do nonthing, if discharge, excess crying or redness getting worse or constant blinking please show to ophthalmologist