Your child has a right to religious education. For details, see Thüringer Schulgesetz §46 http://www.landesrecht.thueringen.de/jportal/portal/page/bsthueprod.psml?pid=Dokumentanzeige&showdoccase=1&js_peid=Trefferliste&documentnumber=29&numberofresults=31&fromdoctodoc=yes&doc.id=jlr-SchulGTH2003pP46
To summarize the most important points: The religious education is a regular school subject, taught in accordance with the authorities of the religious groups in question and the ministry of education.
If the parents decide that their children should not take part in religious education at school, the child does not have to attend these classes. He or she has to attend ethic classes instead. When a child turns 14, he or she can decide on his or her own if he or she wants to attend religious education at school.