These are brilliant 
In our school, it's the same every year- all the P1's are angels, all the p2's are shepherds, all the P3's are stars, and the "main roles" are doled out among the P4's. Since P1, dd2 (now P3) has had her heart set on the role of Mary, when she reaches the dizzy heights of P4. I have been trying to let her down gently ever since, as I know it is hugely unlikely!
If she is anything like me, she will be the narrator in every play, every year, every time. Sigh. I did kick off once (fed up with being the only one without a costume!) and thereafter I got to be a "narrating angel"- a small but worthwhile victory, I felt.
Just when it seemed to be seeping through to DD1 that she was unlikely to ever be Mary, and that being Mary wasn't such great shakes anyway, last year DD2 was chosen to be Mary in her toddler-group nativity. Poor DD1 had to go and watch it, too- I was proud of how graciously she bore seeing her little sis flouncing around in her lovely shiny Mary costume!
DS on the other hand was meant to be a donkey, but point blank refused to wear a costume, any costume, would only go on stage if I stood in the wings, and then started a fight with a shepherd while the angels sang
Funnily enough, I haven't been asked if he wants a part in this year's nativity...