While on patrol, officers say they saw Ronald Messick, 36, buy the heroin in a hand-to-hand drug transaction.
Police followed his vehicle, and when he parked in the fire lane of the Crossroads Shopping Center, officers approached.
After questioning, police say Messick admitted to having heroin on him. That's when police discovered the little girl in his car.
Messick was arrested and charged with possession with the intent to deliver heroin, maintaining a vehicle for keeping a controlled substance, and unlawfully dealing with a child. He has been arraigned and released on $19,500 unsecured bail.
Messick's daughter was turned over to her mother. Police also notified the Delaware Division of Family Services.