YOU SAID:

i went to my moms car to get keys

INTO JAPANESE

私はママの車に鍵を取りに行きました

BACK INTO ENGLISH

I went to my mom's car to get a key

INTO JAPANESE

母の車に鍵を取りに行きました

BACK INTO ENGLISH

I went to get my mother's car

INTO JAPANESE

母の車を取りに行きました

BACK INTO ENGLISH

I went to get my mother's car