It's simple really: Your kid is born male or female biologically. But their gender as they grow up and learn stuff may not be that. Just let them be who they want to be, and support them for who they are. They are still your child whatever pronouns they prefer. Most kids are cis, but some are not and either is perfectly okay. It does more harm telling them they can't be who they want to be and forcing them to live a certain way than letting them explore and be comfortable in their own skin. If it is such a damn sin, then let God judge, and teach kindness above all else because that is universal.