赤ちゃんはずっとおとなしくしていました。

baby; infant

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

continuously in some state (for a long time, distance); throughout; all along; the whole time; all the way; much (better, etc.); by far; far and away; far away; long ago; direct; straight

obedient; docile; quiet

to do; to cause to become; to make (into); to turn (into); to serve as; to act as; to work as; to wear (clothes, a facial expression, etc.); to judge as being; to view as being; to think of as; to treat as; to use as; to decide on; to choose; to be sensed (of a smell, noise, etc.); to be (in a state, condition, etc.); to be worth; to cost; to pass (of time); to elapse; verbalizing suffix (applies to nouns noted in this dictionary with the part of speech "vs"); creates a humble verb (after a noun prefixed with "o" or "go"); to be just about to; to be just starting to; to try to; to attempt to