The main thing I can say is that both parents need to be involved all the way along. If you are doing as many things as you can, both the mother AND the father, not just going to Mass but doing activities during Advent, Lent, reading the Bible, learning the prayers, saying the Rosary, and talking about your faith all the time, as well as sacramental training, you will have done everything possible to give your children a foundation of faith. After that, every child has free will and sometimes there is absolutely NOTHING a parent can do to guarantee that the child will remain a faithful Catholic.
But as a prodigal who returned to the Church when my 1st son was born (I had been praying through the pregnancy but started going back once he was in the world), I can only thank my devout mother for the 10 years of faith that was her legacy to me. I was away for 20 years but I was always seeking - my spirituality as I would have termed it all those years was still crucial in my life. I just didn't know where to look!
And my husband is a Catholic by form but not by belief, which means he does attend church with us and he has allowed the boys to receive the sacraments and go to Catholic schools, but other than that and mealtime prayers, there is nothing flowing from him to them. He doesn't pray and doesn't relate anything in his life to God, not outwardly. He says he cannot state for sure that he believes God exists. The boys know none of this - as far as I know, they just think he's a private person. I have tried to make up for it but I'm afraid I haven't done as good a job as I wanted to - being the spiritual head of the household just feels all wrong to me. When I was more of a feminist I probably wouldn't have minded but since I got married and got my faith back, I want my husband to take that role. He can't, so there is a constant ache in my heart. The unequally-yoked thing? Yeah, I don't recommend it.
But even if you are unequally yoked, if you face that full-on and don't kid yourself that your husband is going to wake up one day and start doing family devotions, you can still really pass along your faith to the children. You'll have to work harder at it, but you can do it. Never despair, never become worried. Pray to Mary and Joseph and the saints. They are helping us all the time.