Praise be to Allah.
Firstly, we would like to offer our congratulations to you for the blessing that Allaah has bestowed upon you by bringing you into Islam. We ask Allaah to help you to be steadfast in Islam and to die as a Muslim.
Secondly, we do not advise you to prevent having children with your Christian wife, for two reasons:
Having a lot of children is required according to sharee’ah. The Messenger (peace and blessings of Allaah be upon him) said: “Marry women who are loving and fertile, for I will be proud of your great number before the other nations on the Day of Resurrection.” (narrated by Abu Dawood, 1754; al-Nisaa’i, 3175; classed as saheeh by al-Albaani (may Allaah have mercy on him) in Adaab al-Zafaaf, p. 132)
It is not definite that your wife will remain a non-Muslim. Allaah may bless her with Islam as He has blessed you, then you may regret having gotten older without having children to bring up in the right religion and with proper manners.
So we advise you not to prevent having children, and to try to call your wife to Islam – maybe Allaah will bless her with Islam.
If Allaah does bless you with children, then you have to bring them up in the right religion and with proper manners from an early age. This is one of the duties that Allaah requires of you, and your non-Muslim wife has no say in the matter. Allaah says (interpretation of the meaning):
“O you who believe! Ward off from yourselves and your families a Fire (Hell) whose fuel is men and stones” [al-Tahreem 6:66].
The Prophet (peace and blessings of Allaah be upon him) said: “Each of you is a shepherd, and each of you is responsible for his flock… a man is a shepherd of his family and will be asked about those who are under his care…” (narrated by al-Bukhaari, 844, and Muslim, 3408).
And Allaah knows best.