How can a single devil, specified by the definite article (alif and lam), perform multiple actions in different places at the same time, such as urinating and harming children, or is what is meant the human's Qareen (companion Jinn)?

The definite article "al-" (ال) in the word "al-shaytan" (الشيطان - "the Satan" or "the devil") refers to the nature and essence of the genus, not to a specific devil. Every human being has a qarin (companion) from among the devils who whispers to him from birth. The reason for a newborn's cry at birth is a prick from the devil, for a devil is assigned to every child of Adam, meeting him at birth and pricking him in his side out of enmity. The newborn cries from this prick, as stated in the Hadith (definition): "There is no newborn who is born but the devil pricks him, and he cries out loudly from the touch of the devil, except for Mary and her son." The apparent reason for a newborn's cry is its departure from its accustomed environment and its transition to cold air and an unfamiliar place.