infancy; cradle period
Refers to the early, formative stage of something, often used figuratively for the beginning of a movement, technology, or era. Not typically used for a baby's literal infancy.
The internet was still in its infancy.
This technology has left its cradle period and entered the practical stage.
黎明期 also means 'dawn' or 'early days' of something, but emphasizes the very first glimmer of development, whereas 揺籃期 suggests a slightly later, protected nurturing phase.
incunable; incunabulum
Compound of 揺籃 (yōran, 'cradle') and 期 (ki, 'period'). The word 揺籃 is itself a compound of 揺 (yō, 'rock, swing') and 籃 (ran, 'basket'), literally meaning a rocking basket, i.e., a cradle.