Which part of the following sentence needs to be changed?We have been knowing each other since we were children.

Explanation

The correct sentence is: We have known each other since we were children. The word "knowing" is in the present participle form, which is used to form the progressive tenses, such as "is knowing" and "are being known." However, the sentence is not in the progressive tense, so the present participle form of the verb is not correct. The correct verb form to use is the simple past form, which is "knew."