Kaṁsa could not be killed by anyone but Kṛṣṇa; therefore Kṛṣṇa was obliged to kill him. But as far as Kaṁsa's eight brothers were concerned, Balarāma took charge of killing them. Balarāma's mother, Rohiṇī, although the wife of Vasudeva, was not the sister of Kaṁsa; therefore Balarāma took charge of killing all of Kaṁsa's eight brothers. He immediately took up an available weapon (most probably the elephant's tusk which He carried) and killed the eight brothers one after another, just as a lion kills a flock of deer. Kṛṣṇa and Balarāma thus verified the statement that the Supreme Personality of Godhead appears in order to give protection to the pious and to kill the impious demons, who are always enemies of the demigods.
(Krsna Book).

The demigods from the higher planetary systems showered flowers, congratulating Kṛṣṇa and Balarāma. Among the demigods were powerful personalities like Lord Brahmā and Lord Śiva, and all joined together in showing their jubilation over Kaṁsa's death. There were beating of drums and showering of flowers from the heavenly planets, and the wives of the demigods danced in ecstasy.
(Krsna Book).

Since Kṛṣṇa was kind and affectionate to His aunts, He solaced them as far as possible. The ritualistic ceremonies performed after death were then conducted under the personal supervision of Kṛṣṇa because He happened to be the nephew of all the dead princes. After finishing this business, Kṛṣṇa and Balarāma immediately released Their father and mother, Vasudeva and Devakī, who had been imprisoned by Kaṁsa. Kṛṣṇa and Balarāma fell at Their parents' feet and offered them prayers. Vasudeva and Devakī had suffered so much trouble from Kaṁsa because Kṛṣṇa was their son.
(Krsna Book).

After creating this situation by His yogamāyā, Kṛṣṇa, appearing with His elder brother, Balarāma, as the most illustrious son in the dynasty of the Sātvatas, very submissively and respectfully addressed Vasudeva and Devakī: "My dear father and mother, although you have always been anxious for the protection of Our lives, you could not enjoy the pleasure of having Us as your babies, as your growing boys and as your adolescent youths." Kṛṣṇa indirectly praised the fatherhood of Nanda Mahārāja and motherhood of Yaśodā as most glorious because although He and Balarāma were not their born sons, Nanda and Yaśodā actually enjoyed Their childhood pastimes. By nature's own arrangement, the childhood of the embodied living being is enjoyed by his parents. Even in the animal kingdom, parents are found to be affectionate to their cubs. Being captivated by the activities of their offspring, they take much care for their well-being. As for Vasudeva and Devakī, they were always anxious for the protection of their sons, Kṛṣṇa and Balarāma. That is why Kṛṣṇa, after His appearance, was immediately transferred to another's house. Balarāma was also transferred, from Devakī’s womb to Rohiṇī’s womb.
(Krsna Book).

Vasudeva and Devakī were full of anxieties for Kṛṣṇa's and Balarāma's protection, but they could not enjoy Their childhood pastimes. Kṛṣṇa said, “Unfortunately, being ordered by Our fate, We could not be raised by Our own parents to enjoy childhood pleasures at home.
(Krsna Book).

When the Supreme Personality of Godhead was speaking as an innocent boy in very sweet words, Vasudeva and Devakī became captivated by parental affection and embraced Him with great pleasure. They were amazed and could not speak or answer the words of Kṛṣṇa but simply embraced Him and Balarāma in great affection and remained silent, shedding incessant tears.
(Krsna Book).

Mahārāja Ugrasena belonged to the Bhoja dynasty; therefore Kṛṣṇa indirectly declared that the King of the Bhoja dynasty would be the emperor of the other small kingdoms. Kṛṣṇa willingly asked Mahārāja Ugrasena to rule over Himself and Balarāma because They were his subjects.
(Krsna Book).

All the kings in the neighboring area had left their homes in fear of Kaṁsa and were living in distant parts of the country. Now, after the death of Kaṁsa and the reinstallment of Ugrasena as king, the neighboring kings were given all kinds of presentations and comforts. Then they returned to their respective homes. After this nice political arrangement, the citizens of Mathurā were pleased to live in Mathurā, being protected by the strong arms of Kṛṣṇa and Balarāma. On account of good government in the presence of Kṛṣṇa and Balarāma, the inhabitants of Mathurā felt complete satisfaction in the fulfillment of all their material desires and necessities, and because they saw Kṛṣṇa and Balarāma daily, face to face, they soon forgot all material miseries completely. As soon as they saw Kṛṣṇa and Balarāma coming out on the street, very nicely dressed and smiling and looking at the citizens with grace, the citizens were immediately filled with loving ecstasies simply by seeing the personal presence of Mukunda. The name Mukunda refers to one who can award liberation and transcendental bliss. Kṛṣṇa's presence acted as such a vitalizing tonic that not only the younger generation but even the old men of Mathurā became fully invigorated with youthful energy and strength by regularly seeing Him.
(Krsna Book).

Nanda Mahārāja and Yaśodā were also living in Mathurā because Kṛṣṇa and Balarāma were there, but after some time they wanted to go back to Vṛndāvana. Kṛṣṇa andBalarāma went before Nanda and Yaśodā and very affectionately embraced them, and then the two Lords spoke as follows: “Dear father and mother, although We were born of Vasudeva and Devakī, you have been Our real father and mother, because from Our very birth and childhood you raised Us with great affection and love. Your affectionate love for Us was more than anyone can offer one's own children.
(Krsna Book).

Dear father and mother, We know that you will feel separation upon returning to Vṛndāvana and leaving Us here, but please rest assured that We shall come back to Vṛndāvana just after giving some satisfaction to Our real father and mother, Vasudeva and Devakī, and Our grandfather and other family members.” Kṛṣṇa and Balarāma thus satisfied Nanda and Yaśodā by sweet words and by presentations of various kinds of clothing, ornaments and copper utensils. They satisfied them, along with their friends and neighbors who had come with them from Vṛndāvana to Mathurā, as fully as possible. On account of excessive parental affection for Balarāma and Kṛṣṇa, Nanda Mahārāja felt tears in his eyes, and he embraced Them and started with the cowherd men for Vṛndāvana.
(Krsna Book).

After this, Vasudeva had his sons initiated by sacred thread as the token of second birth, which is essential for the higher castes of human society. Vasudeva called for his family priest and learned brāhmaṇas, and the sacred thread ceremony of Kṛṣṇa and Balarāma was duly performed. During this ceremony, Vasudeva gave various ornaments in charity to the brāhmaṇas and endowed them with cows decorated with silken cloths and golden ornaments. Then Vasudeva remembered the cows he had wanted to give in charity to the brāhmaṇas after the birth of Kṛṣṇa and Balarāma. But being imprisoned by Kaṁsa at that time, Vasudeva had been able to do so only within his mind, for Kaṁsa had stolen all his cows.
(Krsna Book).

With the death of Kaṁsa his cows were released, and now Vasudeva gave the actual cows to the brāhmaṇas. Then Balarāma and Kṛṣṇa were duly initiated with the sacred thread ceremony, and They repeated the chanting of the Gāyatrī mantra. The Gāyatrī mantra is offered to disciples after the sacred thread ceremony, and Balarāma and Kṛṣṇa properly discharged the duties of chanting this mantra. Anyone who executes the chanting of this mantra has to abide by certain principles and vows. Although Balarāma and Kṛṣṇa are transcendental personalities, They strictly followed the regulative principles. They were initiated by Their family priest, Gargācārya, usually known as Garga Muni, the ācārya of the Yadu dynasty.
(Krsna Book).

According to Vedic culture, every respectable family has an ācārya, or spiritual master. One is not considered a perfectly cultured man without being initiated and trained by an ācārya. It is said, therefore, that one who has approached an ācārya is actually in perfect knowledge. Lord Kṛṣṇa and Lord Balarāma are the Supreme Personality of Godhead, the master of all education and knowledge. There was no need for Them to accept a spiritual master, or ācārya, yet for the instruction of ordinary men They also accepted a spiritual master for advancement in spiritual knowledge.
(Krsna Book).