A security guard was busted for allegedly molesting two young sisters at an Upper West Side migrant shelter Monday evening, law enforcement sources said. Alleged creeper Oscar Delgado, 38, inappropriately touched both the 11-year-old and 8-year-old siblings in the hallway of the shelter on West 88th Street near Riverside Drive some time around 7 p.m., according to cops and sources. Delgado approached the kids as they were playing and allegedly squeezed the buttocks of the older girl, fondled her and attempted to put his hands in her pants, authorities said. The sicko then allegedly turned to the younger sister, touching her vagina over her clothing, cops said.The older girl reported the disturbing behavior to her mom, who called 911, sources said. Both girls — who had been staying at the shelter — were taken to Mount Sinai Morningside for treatment.Delgado was arrested on scene and faces charges including sexual abuse, forcible touching and acting in a manner injurious to a child, authorities said. The facility – formerly used as the New York Institute of Technology’s Riverside Terrace Residence Hall – opened last year as an emergency shelter amid the migrant crisis, The Post reported at the time. The building had a capacity of 125 rooms....