A sick baby should not be crawling around a classroom floor. Did this mother even know what the baby was sick with? She had no problem with the teaching assistant caring for the baby. What does she do about feeding the baby when she does not bring her to the classroom? I guess staying home with her sick child was out of the question.
Babies with fevers are nothing to be concerned about. Unlike adults, infants become feverish with the slightest provocation. Infants with fevers do not need to be rushed to the doctor, and do not need to be kept away from healthy people. Unless the fever is accompanied by other symptoms such as pronounced lethargy which obviously was not the case here, there is nothing to worry about.