Kamsa's demons harassed children throughout the region for fifteen years. Magically, Krishna and Balarama killed them all as part of their divine play, or lila. Thus, the inhabitants of Vrindavana were thankful, remembering their guru's prediction about Krishna. After Krishna killed the arista (bull) demon, the great sage Narada Muni went to Kamsa's palace and told him that Krishna and Balarama were the seventh and eighth sons of Vasudeva. Narada described the events that took place on the night of Krishna's birth and confirmed that Kamsa would meet his death at Krishna's hands.
On hearing this news, Kamsa imprisoned Devaki and Vasudeva again and renewed his vow to kill Krishna and Balarama. He called for the Keshi demon, and other great demons, and just in case that didn't work, he planned to draw the boys into a wrestling match with two of his strongest wrestlers. He sent his servant Akrura to bring the boys back to Mathura. This would be Krishna and Balarama's transition into adulthood, because they never again return to the lighthearted pastimes of their youth, playing in the pastures or dancing with the young gopis.
Kamsa was delirious with fear waiting for Krishna to arrive, and unable to sleep through the night because of bad dreams. He saw his headless body in a mirror, everything appeared double, and he saw the covering of the sky as pierced. He saw holes in his shadow and left no footprints when he walked.
Krishna and Balarama entered the splendorous city with their friends. By and by they came to the wrestling ring and accepted the challenge to fight Kamsa's demons. After fighting for a few moments, Krishna and Balarama easily killed their opponents. Everyone except Kamsa rejoiced at the wonderful defeat. The evil king stopped the celebration and shouted: "Drive the two wicked sons of Vasudeva out of the city! Confiscate the cowherds' property and arrest that evil man Nanda! Kill that ill-motivated Vasudeva! Also kill my father, Ugrasena, along with his followers, who have sided with our enemies."
Krishna jumped into the stands, seized Kamsa, knocked off his crown and dragged him to the wrestling mat by his hair. There He easily killed Kamsa, striking him with His fist. Kamsa's eight younger brothers attacked Krishna and Balarama, but Balarama easily killed them with his club. Krishna and Balarama met their parents, but Devaki and Vasudeva were struck with awe seeing the prophecy fulfilled, and because of a feeling of reverence they were afraid to embrace their sons. After that incident, Krishna and Balarama entered the gurukula and became princes in the court of Yadu.