I believe your desire to have a baby is a God-given one, and one that will serve as a powerful motivator to help you quit. As far as relapsing is concerned, I've done the same many times, and the feelings of remorse and regret that I encounter the next day are sometimes nearly unbearable. These feelings are healthy, however; they remind you that God is calling you to repentance, that He wants desperately a new way of life for you in which you shed old habits and trust in His ability to transform. Two important things: 1) Truly repent. True repentance is prayer for God's forgiveness with the firm intention that you will never again fall into the sins of which you are repenting. 2) If you do fall, the important thing is to pick yourself up and resolve with God's help to keep fighting. It is said that "saints are merely sinners who keep trying." The worst thing you can do (and the thing which the Devil most desires) is that you resign yourself to sin with the attitude that "it's just too hard." Remember, with God, nothing is impossible. Just a few reflections from my own struggles; I hope this helps. I will continue to pray for you.
God bless,
Chris