SB 10.15.1

śrī-śuka uvāca
tataś ca paugaṇḍa-vayaḥ-śrītau vraje
 babhūvatus tau paśu-pāla-sammatau
gāś cārayantau sakhibhiḥ samaṁ padair
 vṛndāvanaṁ puṇyam atīva cakratuḥ
Word for word: 
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; tataḥ — then; ca — and; paugaṇḍa vayaḥ — the age of paugaṇḍa (years six to ten); śritau — attaining; vraje — in Vṛndāvana; babhūvatuḥ — They (Rāma and Kṛṣṇa) became; tau — the two of Them; paśu-pāla — as cowherds; sammatau — appointed; gāḥ — the cows; cārayantau — tending; sakhibhiḥ samam — along with Their friends; padaiḥ — with the marks of Their feet; vṛndāvanam — Śrī Vṛndāvana; puṇyam — auspicious; atīva — extremely; cakratuḥ — They made.
Translation: 
Śukadeva Gosvāmī said: When Lord Rāma and Lord Kṛṣṇa attained the age of paugaṇḍa [six to ten] while living in Vṛndāvana, the cowherd men allowed Them to take up the task of tending the cows. Engaging thus in the company of Their friends, the two boys rendered the land of Vṛndāvana most auspicious by imprinting upon it the marks of Their lotus feet.
Purport: 

Lord Kṛṣṇa wanted to encourage His cowherd boyfriends, who had been swallowed by Aghāsura and then stolen by Lord Brahmā. Therefore the Lord decided to bring them into the palm-tree forest called Tālavana, where there were many delicious ripe fruits. Since Lord Kṛṣṇa’s spiritual body had apparently grown slightly in age and strength, the senior men of Vṛndāvana, headed by Nanda Mahārāja, decided to promote Kṛṣṇa from the task of herding calves to the status of a regular cowherd boy. He would now take care of the full-grown cows, bulls and oxen. Out of great affection, Nanda Mahārāja had previously considered Kṛṣṇa too small and immature to take care of full-grown cows and bulls. It is stated in the Kārttika-māhātmya section of the Padma Purāṇa:

śuklāṣṭamī kārttike tu
 smṛtā gopāṣṭamī budhaiḥ
tad-dinād vāsudevo ’bhūd
 gopaḥ pūrvaṁ tu vatsapaḥ

“The eighth lunar day of the bright fortnight of the month of Kārttika is known by authorities as Gopāṣṭamī. From that day, Lord Vāsudeva served as a cowherd, whereas previously He had tended the calves.”

The word padaiḥ indicates that Lord Kṛṣṇa blessed the earth by walking on her surface with His lotus feet. The Lord wore no shoes or other footgear but walked barefoot in the forest, giving great anxiety to the girls of Vṛndāvana, who feared that His soft lotus feet would be injured.