The other day we were at the library and my son asked another little boy a question (in English). The little boy stared back at him without responding. The boy's big sister came to his rescue - "He doesn't speak English yet. Just Spanish" But she obviously did. I asked her "But you speak English and Spanish?" She emphatically nodded with a great big smile on her face. She is obviously proud of her bilingualism.
Others may not feel so proud and willing to share their bilingualism.
In the past, many immigrants to this country tried to shed their foreign culture, accent and language and become "American." I have a friend who spoke 4 languages at home (2 Filipino dialects, English and French) up until starting kindergarten. When she was asked to speak to a teacher in Tagalog, she couldn't because that language wasn't spoken in her home. Her teacher took this as disobedience and her parents were called. The end result was that her family stopped speaking their native languages at home in an effort to improve her English and help her fit in. What a shame that they felt pressured to obscure their Filipino heritage.
Being bilingual (or multilingual) shouldn't be something to hide.
Being bilingual says something about who someone is - about where they come from and what they value.
If you try to hide this, you miss out on the whole person. The picture just isn't complete. The shame a child will feel due to hiding his family's heritage will surely turn him away from his roots and make him try to become someone he isn't.
Teach your kids that being bilingual is special.
Tell them about where the family comes from and how these languages came to be in your family. Make sure they understand why you've chosen to teach them two (or more) languages. Did you have relatives in another country? Did the family emigrate at one time? Did someone learn a language in school and decide to make it part of the home? These are fascinating topics for kids and help them see their place in the context of the larger world.
The good news is that my friend still speaks 3 of the 4 languages she grew up. She didn't lose out on that piece of her background. However, she was quite pained when discussing it with me. The little girl at the library shares none of this pain. Make sure your kids value knowing German just as much. The more they love it, the better they will do and the more likely they are to pass it on to the next generation.