I went to the dentist on our day off on Friday. I was a good girl.
I went to see a dentist on Friday when we didn't have school. I didn't cry either.
幼稚園児が話しているなら、次のように言うと良いかと思います。
ーI went to the dentist on our day off on Friday. I was a good girl.
「金曜のお休みの日に歯医者に行ったよ。私、いい子だったよ」
to go to the dentist で「歯医者に行く」
day off で「休みの日」
ーI went to see a dentist on Friday when we didn't have school. I didn't cry either.
「学校のない金曜日に歯医者に行ったよ。泣かなかったよ」
to see a dentist で「歯医者に行く」
ご参考まで！
カナダ 
