Why 'das Mädchen' (the girl) is grammatically neuter.
Grammatical gender in German is about word form, not biology. All diminutives ending in -chen and -lein are neuter: das Häuschen, das Fräulein, das Mädchen (from 'Magd', maid). Equally regular: nouns with the endings -ung, -heit, -keit, -schaft are always feminine. Many nouns thus reveal their gender through their ending, not through their meaning.
Useful: Learn endings instead of single words and you'll guess the article right most of the time.
Source: en.wikipedia.org