"我坐在爸爸和妈妈的中间。"

Translation: I am sitting in between my father and mother.

[Alf42]

"I am sitting in between Mom and Dad" was marked incorrect.

[Jas652915]

Because you ignored the heirarchy used in Chinese language, men/elder coming first. Of course your meaning is the same.

[Ayvah01]

But in English, mother always comes before father.

[Vesane]

I sit in between my father and mother - a common theme with all these Chinese ones is it's not taking into account how ambiguous tense/voice is, like present vs present participle (I sit between my mum and dad vs I am sitting between).
Aditionally, 妈妈/爸爸 should really be mum/dad whilst mother and father would be 母亲/父亲

[prabhavati]

I am seated between my father and my mother marked wrong

[Xinmei20]

I am sitting in between my father and my mother was marked incorrect

[jim140738]

"i am sitting in between my father and my mother"
"i am sitting in between dad and mom"