Since the children start to learn the cello from the age of 3 - 4 years at The Cello Corner when they typically don't read or write yet, they also don't read music yet.
At a later stage, however, when they are halfway through the first book, they do start reading music.
Later, once the child starts to play in other positions than just the first position we use 'Position Pieces' by Rick Mooney. The children enjoy playing this book as it contains quizzes which helps them understand and memorize the geography on the cello and the duos for two cellos can be sight read, every chapter concentrating on one new position.
Musicianship is part of the group lessons as it makes learning new pieces easier and makes the whole concept of music clearer.
Material used is 'Hey Presto! Music Theory for Cellists'.
For the younger children (4-5 years old) we use Theory Made Easy For Little Children.
Aural training is considered very important. It starts of course right at the beginning.
You can find where to buy the books here.