Does anybody know why Mädchen (girl in German) is not considered female?
The ending "-chen" is a diminutive for nouns to point a smaller or cuter version of something. It's the same with the ending "-lein", by the way. The words containing these endings are always neuter.
Grammatical gender has absolutely nothing to do with biological gender. It just is.
Nope, that is not right! Grammatical gender has everything to do with biological gender for people as much as for animals, not always for professions, though. Mädchen is the diminutive of Maid, die Maid, which is an old fashion word for Mädchen and which is not used in German for a girl. By adding - chen the article changes into das but every male living creature has the article "der" and every female living creature has the article "die". You might wonder why "das Kind" or "das Baby" is neuter, or why "der Säugling" has the male article, that's because they are superordinated word of a word family, "der Säugling" can be either "der Junge" or "das Mädchen".
Mädchen is modern High German and comes from the early modern High German Mägdchen and Mägdchen comes from the middle High German Magd and Magd comes from the old High German Magad and Magad comes from the Germanic word Magaþi wich means virgin.
By the way the modern High German word Junge goes back to the Germanic word Knab wich was the name of a "spanking stick".
... and therefore the grammatical genders are called 'masculine' and 'feminine' (and neuter), not 'male' and 'female'.
I believe it's the diminutive of Maid (old German for woman). Diminutives are always neutral.
Words ending in chen tend to be neutral, like das Eichhörnchen (the squirrel).
In addition to what wombatua has just said: All words that end with -chen are neuter. It is a diminutive, that refers to "little" or "cute" persons or things.
it is so in some other languages too... I always understood it the way that it is a girl = kid... and kid is neuter too, since you don't care so much if it's a girl or a boy when it's a little kid... Also historically... boy would be considered more important... whereas der Junge.. while a girl was "just a kid" == neuter (I am a girl by the way and am not bothered by this :-)
I don't think your interpretation is true - at least not for German. The reason why Mädchen is neuter is that it is a diminutive form (see other comments).
What I meant more.. was how to help remember it :-) ... more than what is the ACTUAL reason... because nobony knows anymore anyway, we can only speculate about it
This is because Das Mädchen is the diminutive form of Die Magd ("the maiden", in old german), and diminutive is always neuter. Nowadays the original form is no longer used, only the diminutive form ("the little maiden"). For obvious reasons I supose.