It's a tough call, but I wouldn't want anyone telling me what to teach my children. So yeah, you can teach them whatever you want. In the future, you and/or your child will benefit and/or suffer from the consequences of whatever you taught (or failed to teach) them.
Don't feel bad when people laugh at your child because you taught them the earth is a thousand years old or if they kill themselves because you don't love them just the way they are.
If you disagree with the parents, you can always advocate from the outside and ensure everyone has access to an effective, secular education. Children ask a lot of questions too.
