Daniel Pisco, 29, of Vernon, was charged with harassment after the Tuesday incident, The (Newark, N.J.) Star-Ledger reported.
Authorities said Pisco approached the boy in the bathroom of a Walgreen's pharmacy while the boy's mother waited outside.
Pisco left the bathroom and walked quickly toward the front of the store, alerting the boy's mother, who then checked on her son. The boy told her Pisco asked him to urinate into a cup.
The mother confronted Pisco in the store's parking lot, but he denied any involvement and fled the scene.
The mother managed to write down Pisco's license plate number and call police, who arrested the man later.
Police said Pisco pleaded guilty to possession of a controlled dangerous substance this year and believed he was going to have to submit to a urine screening later Tuesday.
Police credited the woman for "for her immediate, quick-thinking response which contributed to identifying," the suspect, police said in a news release.
Mathematician offers formula for finding the perfect Christmas tree
Video of Victoria’s Secret models trying to 'twerk' hits Instagram