I'm thankful for your sons' interest, and I hope you will do everything you can to encourage them and assure them that God cares for them. Can anything be more important than pointing our children toward God?
Yes, children can be very curious, and sometimes they can ask far more questions than we can ever answer (not just about God, but about everything else!). Don't feel that you always have to give a full, detailed answer to their questions about God, however; often a simple answer will satisfy them and even be more understandable. When you don't have an answer, be honest and admit it. Simply tell them that they have asked a very good question, and perhaps they can help you find an answer.
Remember too that children learn not just from what we say but by what we do. Do your sons sense that God is real to you and your husband, and do they see that He makes a difference in the way you live? Do they hear you pray and see you read your Bible? The apostle Paul took care how he lived "in order to make ourselves a model for you to follow" (2 Thessalonians 3:9).
Is Christ the center of your life, both as an individual and as a family? For your own sake, as well as the sake of your children, make sure of your commitment to Christ. Then ask Him to help you be examples of faith to your sons, so that someday they too will put their faith and trust in Christ.