YOU SAID:

i saw my mom banging my cousin

INTO JAPANESE

お母さんがいとこを叩いているのを見た

BACK INTO ENGLISH

I saw my mom hitting my cousin

INTO JAPANESE

お母さんがいとこにぶつかるのを見た

BACK INTO ENGLISH

I saw my mom hit my cousin

INTO JAPANESE

お母さんがいとこにぶつかるのを見た

BACK INTO ENGLISH

I saw my mom hit my cousin