being christmas, you should also find some nice childrens christmas books about christian traditional christmas.
Also, check out your church, they should have some reading info, and as you boys get older, your local church may do nativity scenes, and re-enactments etc to help explain things to them.. (esp at Easter as well.) Perhaps even Sunday school may be an option for you.
If you have any questions thou, or want to discuss any thing, i am sure in my 6 years of living in a convent (ie.. boarding school) will come to some use..