All the gopis, headed by mother Yasoda, were bound by maternal affection. After they thus chanted mantras to protect the child (Krsna), mother Yasoda gave the child the nipple of her breast to suck and then got Him to lie down on His bed - SB 10.6.30

Expressions researched:
"All the gopīs, headed by mother Yaśodā, were bound by maternal affection. After they thus chanted mantras to protect the child, mother Yaśodā gave the child the nipple of her breast to suck and then got Him to lie down on His bed"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

Śrīla Śukadeva Gosvāmī continued: All the gopīs, headed by mother Yaśodā, were bound by maternal affection. After they thus chanted mantras to protect the child, mother Yaśodā gave the child the nipple of her breast to suck and then got Him to lie down on His bed.

SB 10.6.30, Translation and Purport

Śrīla Śukadeva Gosvāmī continued: All the gopīs, headed by mother Yaśodā, were bound by maternal affection. After they thus chanted mantras to protect the child, mother Yaśodā gave the child the nipple of her breast to suck and then got Him to lie down on His bed.

When a baby drinks milk from the breast of his mother, this is a good sign of health. So the elderly gopīs were not satisfied with chanting mantras to give protection to Kṛṣṇa; they also tested whether their child's health was in order. When the child sucked the breast, this confirmed that He was healthy, and when the gopīs were fully satisfied, they had the child lie down on His bed.