Foreign Language

Get some children's books in German, like The First 1000 Words in German. That one also has a sticker book. Or Dr Suess in German.
Go to an authentic German restaurant and check out the menu.
Learn a phrase a week. Like this week's is Auf Wiedersehn--Good Bye or Bitte- Please. Then use it daily. Add on, so don't just stop saying Bitte, keep that one up while you learn another.
Make it a family project
Languages have to be used to retain them. Rosetta Stone is expensive but supposedly pretty good. Some high schools will use it for their online language classes.
Get a foreign exchange student from Germany, they are very nice people and it is an excellent way to learn about the country and language.

There are free online programs that you can try out, rather than spend money on something that doesn't work. Or your local library may carry muzzy, mine does.

My dd has been using Tell Me More which is essentially a generic version of Rosetta Stone. While the introductory disc was great, once she got into the lessons themselves she said it was very confusing and disorganized. She didn't have a clue what was going on. Try to find someone who speaks the language and can teach a true immersion method.

I did not like Muzzy. My 2 yr old was frightened by the characters but your 8 yr old might be ok with it. Luckily, I borrowed it from the library and could return it without investing in something so expensive. It just seemed unpractical to me. It's not something that would teach a kid how to have a conversation in a foreign language, in my opinion. Maybe just some common words. Overall, I think Muzzy is overpriced.

My sister used Rosetta Stone to learn chinese before she went to work in China. She said it was ok and she's an adult, so I don't know can't comment on how it would work for kids.

I would check out your local library first and see if they have either programs. That way, you can try it out before shelling out big bucks to actually purchase the program.