Sounds a bit wishy-washy so far. Go back to basics: WHY are you doing these workshops, i.e. what is the purpose, what are you aiming to achieve? That's what will guide you.

If it is empowerment, get them to sing in a style they are not familiar with (or even to sing at all). Or to play an instrument they only spend 30 mins learning.

If it is listening skills, get them to focus attention on a 28-verse ballad, then tell you the story they heard.

If it is communication, get them to write a poem/song about their everyday working life, to relate a real story.

If it is environment, concentrate on music made by nature (there are albums you can get for that), getting them to guess the sources of the sounds.

But to simply dive in full of excitement without a purpose risks everything from irrelevance to ridicule.

So - go back to basics.