Lord Sri Krsna, having Himself become the cowherd boys and groups of calves, maintained Himself by Himself. Thus He continued His pastimes, both in Vrndavana and in the forest, for one year - SB 10.13.27

Expressions researched:
"Lord Śrī Kṛṣṇa, having Himself become the cowherd boys and groups of calves, maintained Himself by Himself. Thus He continued His pastimes, both in Vṛndāvana and in the forest, for one year"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

In this way, Lord Śrī Kṛṣṇa, having Himself become the cowherd boys and groups of calves, maintained Himself by Himself. Thus He continued His pastimes, both in Vṛndāvana and in the forest, for one year.

SB 10.13.27, Translation and Purport

In this way, Lord Śrī Kṛṣṇa, having Himself become the cowherd boys and groups of calves, maintained Himself by Himself. Thus He continued His pastimes, both in Vṛndāvana and in the forest, for one year.

Everything was Kṛṣṇa. The calves, the cowherd boys and their maintainer Himself were all Kṛṣṇa. In other words, Kṛṣṇa expanded Himself in varieties of calves and cowherd boys and continued His pastimes uninterrupted for one year. As stated in Bhagavad-gītā, Kṛṣṇa's expansion is situated in everyone's heart as the Supersoul. Similarly, instead of expanding Himself as the Supersoul, He expanded Himself as a portion of calves and cowherd boys for one continuous year.