Religion has many divisions of teachings and Public School Teachers are NOT qualified to teach religion except generally. If Religion is taught it should be taught as part of a many religion course that also includes the many religions around the World.
If parents want their children taught Christianity, they should enroll them in a school that teaches their division choice. Not all Christians are Catholic. Also, parents can take their children to their Church of choice as well. There are other organizations to choose from as well … like camps, daily vacation Bible School, etc.