All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If your wife is as you mentioned, a chaste and good woman who does not try to influence your children in a bad way, and you do not fear that she causes harm to them as far as their religion, Islam, is concerned, then you are not asked to divorce her. We think that you should keep her and deal with her kindly. Call her to Islam orally and through practical Islamic acts, raise your children in an Islamic way, and try your best to protect them from the Christians’ doubts and evil acts.
Allah knows best.