Essentially you're saying that a German citizen can only freely express themselves in a way the government deems appropriate.
I think you miss the essential point here: Germany was fortunately liberated in 1944/45 by the Allies. The Allies enforced the process of Denazification, which envolved several actions, first and foremost the removal of Nazi symbolism of official buildings, renaming of streets and places which the Nazis had given names of their own (mostly Hitler's). The Allies were keen to prevent any uprising of Nazi terror once and for all. So, since 1949, the year when both German states were founded, the Germans (in the West as well as in the East) decided to make it a prime directive of their policy to keep fascism down. So, your freedom of speech in Germany is protected by the state, as long as you do not praise Nazism or deny the existence of the Holocaust. That's it. And the reason is not censorship as such, but a very special, mostly German and Austrian, responsibility to keep a promise that was given after 1945: not to let facism rise a again on German soil.
From what I can tell Germany's general legislation seems to be more of a "Think of the children!" rather then focused on liberty.
The fact that children aren't allowed to buy/consume things that adults may, is a quite different discussion. For example, people under 18 aren't allowed to consume pornography as well as hard alcoholic beverages (beer is allowed for everyone under 17, hey they're the Germans :-) ). I think, you would call it a violation of the freedom of speech, when your six-year old is kept from buying a bunch of sex-magazines on his way home from school.
Nazi symbolism is forbidden for any German, regardless of age, sex, profession, belief, etc. It may only depicted for educational reasons (museums or historic textbooks, as far as I know). The spreading of "Mein Kampf", Hitler's first book, is for example not forbidden by the state, but of the current copyright holder.
By the way: Have you ever been Germany or Europe, at least?