21:27
@ChristianSauer, I think most of what I could contribute has been mentioned in one way or another in the answers, but maybe another perspective/other wording might be useful. I am in a similar situation. I live in Bavaria (quite traditional), and if my son (7) went to a non-religious Kindergarten, my daughter is attending a Catholic one (better from a logistic point of view). You should know that the influence of the religion does not stop at the Kindergarten.
It might also be useful for you or some commentators to know that religion is part of the curriculum of the German school
Some schools offer other choices, the strict minimum in Bavaria is a choice between Roman Catholic, Evangelist or... Ethic (not religious).
So Kids would still learn about ways to behave in society, without the precepts of the religions. But, during the first year, they studied the lifes of Jesus, Martin, Nicholas, and a few others. As they are needed to understand the holidays that rhythm the calendar.
But back to your issue, I think you should clarify to yourself what are your intentions: do you want to teach atheism (or your version of it), or let your child decide for themselves once they are old enough?
Because, the freedom to choose imposes that they have a good understanding of both sides. And seeing that you can and probably will provide one side, you should also ensure they get the other one.
Otherwise, you take that choice for them. In the same way that very religious people do by bringing their kids to Church every weeks, and limiting their extra-scolar activities to religious-only groups.
I'm not judging, just pointing out.
What we try to do for our parts, is discussing it with them. Well only with my son as my daughter is still too young. I have had a few discussions with my son as I was the one to introduce him to the concept of God and religions (many churches around, and kids are curious).
Thus I tried to explain what God could be for many people, stating that neither existence not inexistence can, in the current state of our knowledge, be soundly proven. Therefore people are free to decide for themselves what to believe.
And only then I pointed out that me and my spouse did not, in fact, believe in that existence.
My son usually answers that he, for himself do believe in it. But that's mostly the influence of his friends... not any teacher.
And we do not make a big story out of it. Just saying that whatever he decides, he should really think about it.
But I know that my spouse had a lot of mandatory religious education as kid, but yet ended up atheist. Family has probably more influence that you may believe.