What about teaching them about the different kinds of books in the bible? There's history, law, letters, proverbs, songs, poetry etc etc etc. I've done a thing where the different books have been written on cards and they've had to order them. I saw something once where they each make a book of the bible out of a cereal box (ie decorate the spine) and then you put them all together to make a complete bible.
Or a bible duel where you tell them something to find and they race to be the first one to get it. If they aren't used to the bible then I wouldn't give them a full bible reference, but I'd ask them for, say, the opening sentence of Isaiah and they have to use the contents page to race to find it. You could then show them how each book is broken up into chapters and have them race to find the opening sentence of, say John chapter 3. And if you really want to go for it then show them the verse references too. But that's quite hard - I did it with year 5 in a Catholic school so they were all familiar (to a greater or lesser extent) and they really find it tough. I've done something similar as a race outside - put them in groups of 2 or 3, with 1 team member having the bible and the other(s) stationed somewhere else. You tell child A a bible reference, they have to remember it and run to the child with the bible, look it up, and then child C has to remember it and run back to you for checking before you give them the next reference.
There are great films of all sorts of bible stories on youtube which you could download to use as a starter. And I think it's important they understand the difference between the old and new testament ie the bit before Jesus which the Jews share quite a bit of, and the Jesus/post Jesus bit. Lots and lots of references in the new testament to the old testament so they could do something with checking one of those.
If you've got them for 4 hours then there must be some drama/art/cooking in there too. I once had my year 1s make unleavened bread (while the year 2s were doing a SATS paper :) ) and then we shared it with some Ribena and re-enacted the last supper. There are loads and loads of battles in the old testament...
Does any of this inspire you?