Choir Builders for Growing Voices does just what the title implies.
The warm-ups are aimed at the younger or growing voice. This book is ideal for singing schools, KS2 & lower KS3 & junior/youth choirs (you may want to make up some of your own words at this level).
There are 18 warm-up/workout songs which teach posture, breathing, flexibility, vocal range and more using unison songs, some of which then divide into optional parts or rounds.
The enclosed CD has demonstration and backing tracks.