Why will you speak to your kids in German? I would only speak them in your mother tongue, since they will learn the local language anyway in the school.
I only speak to my kids in Spanish, my wife only in Polish and Spanish when we are all together. My old daughter went to kinderkrippe in German and now to kindergarten and with almost 7 years speaks really fluent the 3 tongues. If you want them to learn your mother tongue, never talk to them in the local tongue or they will get used to it, and they will like it and will try to avoid your mother tongue