YOU SAID:

I used to play with the red ball with my cousin at my grandparent's farm

INTO JAPANESE

私は祖父母の農場でいとこと一緒に赤いボールで遊んでいた

BACK INTO ENGLISH

I was playing red balls with my cousin on my grandparents' farm

INTO JAPANESE

私は祖父母の農場でいとこと一緒に赤いボールで遊んでいた

BACK INTO ENGLISH

I was playing red balls with my cousin on my grandparents' farm