They are talk about their presents.（改错）

talk---talking

talk---talking

They are talking about their presents.

talking

They are talking about their presents.

这是一道考准确运用时态问题的句子，这句话的意思是“他们在谈论他们的父母”，属于“正在做某事”类型的句子，即现在进行时，其结构是be(am ,is 或are) + 动词的ing形式 。
所以将句中的talk 改成 talking 就正确了。