He (Brahma) could understand that although the original calves and boys were still in the cave where he had put them, Krsna had expanded Himself and so the present demonstration of calves and boys consisted of expansions of Krsna

Expressions researched:
"He could understand that although the original calves and boys were still in the cave where he had put them, Kṛṣṇa had expanded Himself and so the present demonstration of calves and boys consisted of expansions of Kṛṣṇa"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

Then, however, Lord Brahmā saw that the calves and boys he had taken were still in the same mystic māyā into which he had put them. Thus he concluded that the calves and cowherd boys now playing with Kṛṣṇa were different from the ones in the cave. He could understand that although the original calves and boys were still in the cave where he had put them, Kṛṣṇa had expanded Himself and so the present demonstration of calves and boys consisted of expansions of Kṛṣṇa.

SB 10.13.41, Translation and Purport

Lord Brahmā thought: Whatever boys and calves there were in Gokula, I have kept them sleeping on the bed of my mystic potency, and to this very day they have not yet risen again.

For one year Lord Brahmā kept the calves and boys lying down in a cave by his mystic power. Therefore when Brahmā saw Lord Kṛṣṇa still playing with all the cows and calves, he began trying to reason about what was happening. "What is this?" he thought. "Maybe I took those calves and cowherd boys away but now they have been taken from that cave. Is this what has happened? Has Kṛṣṇa brought them back here?" Then, however, Lord Brahmā saw that the calves and boys he had taken were still in the same mystic māyā into which he had put them. Thus he concluded that the calves and cowherd boys now playing with Kṛṣṇa were different from the ones in the cave. He could understand that although the original calves and boys were still in the cave where he had put them, Kṛṣṇa had expanded Himself and so the present demonstration of calves and boys consisted of expansions of Kṛṣṇa. They had the same features, the same mentality and the same intentions, but they were all Kṛṣṇa.