The Salvation Army Nursery is of Christianity background. As I know, the kids will have 15mins morning prayer period everyday which teaches them how to share with others, and love others,......etc. This is to develop them into a better human being. So, you don't need to worry about that.
Even my sister is not a Christian, she still let her son to go to a Christian school since she thinks it is good for his personal growth in all aspects.