Shoot... Why not let it just become a collage of free association images that the kids "create"... The operative word here is create... That's the fun part...

Anything else an' you kinda have a specific outcome in mind and that in itself is inhibiting...

Jus' let the kids "create" this space with no rules other than the obvious considering you are teaching in a Cathlic school... There's still plenty of room fir the kids to do their own thing...

Bobert