John Lewis has a paint your own nativity scene kit on offer for £10 instead of £20. At the time of writing there's still 'more than 10' available, so there should still be plenty of stock. Delivery is £3, and since you probably don't need it for another 50-odd weeks, you can wait five days for delivery, I'm sure.
Just before Christmas the question of where to find a nativity scene suitable for children did the rounds between my friends on Facebook, and a few rather pricey items were floated and toyed with - but few of them really at a child friendly price.
This Scene from John Lewis seems to be pretty good value. You receive a ceramic stable and figures, 12 pots of paint and two paint brushes.
The figures include animals, wise men, angels, Mary and Joseph and the baby Jesus in a crib. If painted nicely, it should be a lovely Scene that could last for many years.