I believe it was a bit of both: a relationship between teachers in a preschool might cause some of the relationship drama that sometimes happens between couples to spill over to the kids and/or influence their behaviors; you don't want your poor innocent kid to suffer, in one way or another, from the fighting or mushing of the teachers in charge, not to mention that the entire relationship enters the question of whether they will have ability to retain their professionalism no matter what happens. Also, you must remember that the guy was the "prince" of the nursery, so having their man-meal be taken away from them by a girl that looks like a cartoon villain would make the mothers a tad bit sour.