This is the 2712th most frequent Korean word.
아이들은
"Children"
This context uses '아이들은' to denote children as the subject of the sentence performing the action of playing.
아이들은 공원에서 놀고 있어요.
The children are playing in the park.
Here, '아이들은' indicates the general group of children who have a preference for reading.
아이들은 책을 읽는 것을 좋아해요.
Children like reading books.
In this instance, '아이들은' refers to the specific group of children involved in the action of walking.