I don't teach music, but I do teach Montessori. I also have some musical training (voice, piano, guitar, violin). Traditional Montessori music lessons are done in the classroom by the Directress and involve singing, clapping rhythms and exposure to different instruments. Also, Montessori developed a musical material to be used by the children daily. Called "The Bells" it is two sets of bells that form an octave from middle C to high C. There are two sets so that first the child learns to match notes before exercises for setting up the notes. This activity involves alot of ear training. A child can learn perfect pitch at this age if he is so interested. There are materials for writing music and for reading music in the Montessori repertoire, as well.
Can you connect with the teachers as far as what music lessons the children have in their classes and trying to support this learning through repetition and extensions such as studying different types of music (music from each continent or classical, jazz, blues) or different composers. Conversely, they can support your lessons by helping the children practice songs.
I agree with Tracy's suggestion to do lots of music involving movement. Remember, you don't always have to have the movements predetermined but you can let the children just "go with the flow". Children learn songs quickly. I would try to follow a pattern as part of your lesson. For example, start each class with the same song to begin the lesson, then do a movement activity, followed by a story about a composer and end with another song.
Another music activity we do is to walk on an elliptical line to different rhythms such as marching, galloping, walking, etc. with music that reflects these rhythms.
We have a listening area where the children listen to cd's and we rotate this to include music from different parts of the world or different instruments, etc. Children gain alot from listening to music - the more you can demonstrate for them, the better - such as singing or playing an instrument. Since, you are such an accomplished pianist, I would definitely include time where the children are sitting comfortably listening to you playing piano.
The music teachers where I work use Kodaly and Orff techniques in their lessons as well.