小孩的哭声怎么说英语

The sound of a crying child is called "crying" or "sobbing" in English. You could also describe the sound as "wailing" or "weeping" if the child is crying very loudly or intensely. For example, you could say:
"I heard the sound of a crying baby coming from the next room."
"The child was sobbing uncontrollably after falling and scraping her knee."
"The wailing of the toddler could be heard throughout the house."
"The weeping of the young child echoed through the hallway as she was being comforted by her mother."