I've worked in small nurseries and large nurseries. The largest was a 180 place setting, the smallest about 30. In a smaller nursery the staff will know all the children and vice-versa. That would be impossible in one of the huge ones. How can the manager remember the names of 200+ children, 400+ parents and hundreds of brothers and sisters?
The number of children in the room is an important factor too. Too many children and the staff have to herd children rather than address them by name when doing things. I worked in a room of 45 pre-schoolers. You lose that personal touch. I would say you should avoid nurseries with more than 12 babies in the baby room(0-2), 16 toddlers in their room (2-3), and more than 26 older children (3+) in the big room, and don't bother with settings with 100+ places.