They are quite casual, and with ESF schools, they are more focusing on the child, instead of the parents.
I think the child need to demonstrate some sense of maturity and also ability and willingness to THINK. Critical thinking and active participation is valued generally in ESF schools.
ESF kindergartens will invite some of the applicants to a "Play Visit" where a parent is expected to accompany his/her child in play and a teacher will come round to talk to each pair of parent/child for a short while, it will be just a quick social chat.
The kindergarten will assess the English ability of the child. If the child is talkative and can express in English, that will be excellent, but if the child is rather quiet like most children under 3 years old are, then it is important for the parent to do most of the talking to demonstrate that the child can understand English and can interact accordingly.
The focus is on the child, but if the child is quiet then the parent becomes an important part, so in a way it can be thought of as 面試家長
Last but not least, do NOT send your helper to do your job of accompanying your child in play just because your helper happens to speak better English, that will almost guarantee a negative outcome.
this is my experience, a group of children (around 10) and their parents entered a classroom, there were a lots of toys and free for your child to play, while the children were busy at playing, 2 teachers came around and talked to the child respectively, the 1st teacher talked to my kid and asked some question about what he was playing, do you like.....etc.
the 2nd teacher came around while I was playing with my kid, she sat next to us, observed what our conservation.