Buy small nativity figures – or the kids can make their own from modelling clay – and build up a traditional nativity tableau piece by piece during Advent.
You can buy wooden nativity figures from craft shops or splash out on fabulous hand-made Ostheimer ones from Myriad - they're expensive but will last for generations. And if you want a more personal touch, it's easy enough to make your own nativity figures - children can model people and animals with oven-hardening modelling materials such as Fimo (from craft shops and Woolworths).
For Advent, wrap the figures up individually in tissue paper and number them from one to 24. Make your stable scene - a black velvet backdrop with gold stars set on a coloured cloth is simple and looks effective. Every day from 1st December, the children unwrap the numbered tissue paper packet of the day and add the figure or animal to build up the nativity scene as the month progresses.
You can also walk Mary day by day along a ‘star path’: a series of 24 gold stars leading to the crib. (After she’s passed, move the star behind her to the nativity background.) Until finally, on Christmas morning, baby Jesus joins the throng.