the sound of birds or insects

鸟儿在树枝上发出啾啾的叫声。

onomatopoeia · a kiss, or the sound of kissing, used in Taiwan or as online slang

她在男朋友的脸颊上啾了一下。

the sound of a child crying or wailing

孩子在摇篮里啾啾地啼哭。