I am learning German and words like das, die, der are confusing me. "The woman" in German is "die Frau" which indicates that "die" is used for females. But then there is "das Mädchen", here we are using "das" for females. Why is this so?
Mädchen is a diminutive. All diminutives are of neuter grammatical gender.
As a general rule: the grammatical gender has nothing to do with the biological gender of the object named by a noun even though both can coincide.
"Chen" is used to indicate that something is "small/cute". Like:
Blättchen (=small leave), Wörtchen (=small word), Häuschen (=small house), Tierchen (=small animal), Dienstmädchen*(= servent girl)* ,Hündchen (=puppy), Schulmädchen(=school girl).
Similarly, girl in english are used to indicate small/cute female, in German girl are referred as "Mädchen". Now we use "das" with words having "Chen", hence "the girl" translates to "das Mädchen".