Take a look around this planet and oppression done in the name of religious superstition, but for a more charitable argument, even if religion is good, children deserve to have a diverse and secular upbringing if we care about the religious freedom of the child.
I'm also German, and here children are essentially mini-citizens, not some sort of property of their parents, with about as much autonomy as a mule. It's not about whether religion is good, it's about whether children have the right to be brought up, from an early age, in an impartial, dvierse and social environment, rather than being indoctrinated by their parents.
the US system doesn't treat children like citizens with autonomy and rights in their own right, but leaves them to the whim of their parents, regardless of what quality of education or values they can provide. That is incomprehensible to me,and I'd argue it actually harms the freedoms and rights of children and their autonomy. It's outright medieval to me to be honest.