This is the 18996th most frequent Korean word.
아기들은
"아기들은" means "babies" or "the babies" in English.
Here, '아기들은' is the subject of the sentence, indicating generally that babies need to sleep well.
아기들은 잠을 잘 자야 해요.
Babies need to sleep well.
In this question, '아기들은' refers to babies in general, asking about their preferences.
아기들은 초코를 좋아하나요?
Do babies like chocolate?
'아기들은' is again the subject of the sentence, emphasizing the actions performed by babies.