In one of his books he really goes into detail about how children treat other children who have difficulties with their new language.

goes 是动词 go 的第三人称单数现在时形式，go 的基本意思是"去、进行"。 into 是介词，表示"进入...状态"或"深入...方面"。 detail 是名词，意思是"细节、详情"。 goes into detail 是一个固定短语，意思是"详细说明、深入描述"，表示对某个主题进行细致入微的探讨。