In this way, after reaching Vṛndāvana, where everyone lives eternally, very peacefully and happily, they encircled Vṛndāvana, drew all the carts together in a half circle, and in this way constructed a temporary residence. When Kṛṣṇa and Balarāma saw the beautiful appearance of Vṛndāvana, Govardhana Hill and the banks of the river Yamunā, They felt very happy. As They grew up They began talking with Their parents and others in childish language, and thus They gave great pleasure to all the inhabitants of Vṛndāvana.
(Krsna Book).

Soon Kṛṣṇa and Balarāma had grown sufficiently to be given charge of the calves. Cowherd boys, from the very beginning of their childhood, are trained to take care of the cows, and their first responsibility is to take care of the little calves. So along with the other little cowherd boys, Kṛṣṇa and Balarāma went into the pasturing ground and took charge of the calves, and there They played with Their playmates. While taking charge of the calves, sometimes the two brothers played on Their flutes. And sometimes They played with āmalaka fruits and bael fruits, just as small children play with balls. Sometimes They danced and made tinkling sounds with Their ankle bells. Sometimes They made Themselves into bulls and cows by covering Themselves with blankets. Thus Kṛṣṇa and Balarāma played. The two brothers also used to imitate the sounds of bulls and cows and play at bullfighting. Sometimes They used to imitate the sounds of various animals and birds. In this way, They enjoyed Their childhood pastimes apparently like ordinary, mundane children.
(Krsna Book).

Once, when Kṛṣṇa and Balarāma were playing on the bank of the Yamunā, a demon of the name Vatsāsura assumed the shape of a calf and came there intending to kill the brothers. By taking the shape of a calf, the demon could mingle with the other calves. Kṛṣṇa, however, specifically noticed this, and He immediately alerted Balarāma about the entrance of the demon. Both brothers then silently approached him. Kṛṣṇa caught hold of the demon-calf by the two hind legs and tail, whipped him around very forcibly and threw him up into a tree. The demon lost his life and fell down from the top of the tree to the ground. When the demon lay dead on the ground, all the playmates of Kṛṣṇa congratulated Him, "Well done! Well done!" and the demigods in the sky showered flowers with great satisfaction. In this way, the maintainers of the complete creation, Kṛṣṇa and Balarāma, used to take care of the calves every day, beginning in the morning, and thus They enjoyed Their childhood pastimes as cowherd boys in Vṛndāvana.
(Krsna Book).

The name of this beast was Bakāsura, and he was a friend of Kaṁsa's. He appeared on the scene suddenly and immediately attacked Kṛṣṇa with his pointed, sharp beak and quickly swallowed Him up. When Kṛṣṇa was thus swallowed, all the boys, headed by Balarāma, became almost breathless, as if they had died. But when the Bakāsura demon was swallowing up Kṛṣṇa, he felt a burning, fiery sensation in his throat. This was due to the glowing effulgence of Kṛṣṇa.
(Krsna Book).

When the boys saw the showering of flowers and heard the celestial sounds, they became struck with wonder. And when they saw Kṛṣṇa freed from the mouth of the great demon Bakāsura, all of them, including Balarāma, were so pleased that it seemed as if they had regained their very source of life. As soon as they saw Kṛṣṇa coming toward them, they one after another embraced the son of Nanda and held Him to their chests. After this, they assembled all the calves under their charge and began to return home.
(Krsna Book).

All the cowherd men, including Nanda Mahārāja, used to talk of the wonderful activities of Lord Kṛṣṇa and Balarāma, and they were always so much absorbed in those talks that they forgot the threefold miseries of this material existence. This is the effect of Kṛṣṇa consciousness. What was enjoyed five thousand years ago by Nanda Mahārāja can still be enjoyed by Kṛṣṇa conscious persons simply by talking about the transcendental pastimes of Kṛṣṇa and His associates.
(Krsna Book).

Thus Balarāma and Kṛṣṇa enjoyed Their childhood pastimes, imitating Lord Rāmacandra's monkeys, who constructed the bridge over the ocean, and Hanumān, who jumped over the water to Ceylon. They used to imitate such pastimes among Their friends and so happily passed Their childhood life.
(Krsna Book).

Aghāsura, thus deciding to kill all the inhabitants of Vṛndāvana, expanded himself by the yogic siddhi called mahimā. The demons are generally expert in achieving almost all kinds of mystic powers. In the yoga system, by the perfection called mahimā-siddhi, one can expand himself as he desires. The demon Aghāsura expanded himself up to eight miles and assumed the shape of a very fat serpent. Having attained this wonderful body, he stretched his mouth open just like a mountain cave. Desiring to swallow all the boys at once, including Kṛṣṇa and Balarāma, he sat on the path.
(Krsna Book).

One day, a few days before a year had passed, Kṛṣṇa and Balarāma were maintaining the calves in the forest when They saw some cows grazing on the top of Govardhana Hill. The cows could see down into the valley where the calves were being taken care of by the boys. Suddenly, on sighting the calves, the cows began to run toward them.
(Krsna Book).

When Balarāma saw this extraordinary exchange of affection between the cows and the calves and between the fathers and their children—when neither the calves nor the children needed so much care—He began to wonder why this extraordinary thing had happened. He was astonished to see all the residents of Vṛndāvana so affectionate to their own children, exactly as they had been to Kṛṣṇa. Similarly, the cows had grown affectionate to the calves—as much as to Kṛṣṇa. Balarāma therefore concluded that the extraordinary show of affection was something mystical, either performed by the demigods or by some powerful man. Otherwise, how could this wonderful change take place? He concluded that this mystical change must have been caused by Kṛṣṇa, whom Balarāma considered His worshipable Personality of Godhead. He thought, "It was arranged by Kṛṣṇa, and even I could not check its mystic power." Thus Balarāma understood that all those boys and calves were only expansions of Kṛṣṇa.
(Krsna Book).