i often hear the sound of children (playing) in the park.请解释为啥用playing?

题目

i often hear the sound of children (playing) in the park.请解释为啥用playing?
为啥用playing,为啥不用to play或者其他答案,是何种用法?并请再举点相似例子

答案

playing表示正在进行,听见的自然是正在进行的,而不是要强调整个过程.所以不能用to play.