On Monday-Wednesday of Holy week. we are organising a three day camp (daytime not night time) with a focus on drama, art and music skills for kids aged 10-14. We will work towards presenting on Wednesday a drama going from the Entrance into Jerusalem, through holy week to the resurrection. It will mostly be narrated, with kids in costumes (which they will make) acting out parts (drama). Some of the narration or parts can be musical.
Any suggestions for music which could be usefully incorporated? This group has no collective musical experience, though some might be in my schola, most will have little or no ability to read music of any sort, and will not know any common body of hymns to draw on, so if you are suggesting please know we are likely to be learning everything from scratch.
I would like to include:
At least one piece of Gregorian chant
At least one chant in English
Something in parts (Could be taize?) which can be done with unchanged voices
One piece of polyphony - any really really simple suggestion appreciated
Some simple rounds, so that we can get singing on something straight away before tackling the harder pieces.
Maybe something that a more accomplished singer could do solo?
Any other ideas at all?

Thanks. Two points - this is not liturgy. Second, we are doing it whether you think it is the worst idea ever or not, so don't waste your time (if you are that way inclined).

Any help appreciated :-)