Hi, my son is in Prep now (equivalent to Y1 at ESF).
There was only one other child in the interview, although I have heard that there can be quite a few more. They want to see a couple of things. First if the child is detressed after leaving their parents (parents are not in the room with them) and if they do get upset, if/how the recover. Second, to see how the play with other children.
My son said that they read a story and had to draw a picture. There were blocks with letters on them that he has to put in order. He has to write his name. I think there was something else but for the life of me, I can't remember.
The interviewer was a teacher. It actually ended up being his teacher this year. It took about 35 minutes.
I hope this helps.