I am an elementary school teacher but have helped school guitar club for Graces 3-5. My opinion: My students were immediately taught chords with small 6-strings and also reading staff music. I think that's a mistake. It takes weeks for them to hold a simple chord that sounds terrible and there's nothing they can do with it.
I think they should be first taught tab and simple single note songs: anything from Mary Had A Little Lamb to the melody of songs they like to listen to be it Justin Bieber or Led Zeppelin. They need to enjoy it and play simple songs right away or it will be a chore and they will drop it.
Then get into reading staff sheet music, understanding time, chords, scales gently. I guess you could also make games early on for them to do trills, repetitive speed exercises. They might like that.