It depends on what you mean by "mistreated": if it was criminal mistreatment, for example (criminal abuse or neglect), then you most likely could not be fired, because firing you in that situation would be retaliation for bringing forward a complaint about a criminal law violation, which is normally illegal.But if it was that other children, staff, etc. were not being "fair" to your child or were even being "mean" to him/her, then they could fire you for complaining. There is no law requiring fairness or preventing staff or other children from being mean; therefore, there is no protection for bringing forward a complaint about such treatment, and you could be terminated.