As a former Primary School Teacher and former actress, I am very comfortable doing events in schools or at festivals.
 am happy to cater to any number of people in an audience.  I have played to audiences of 6 to 600.
If you are a school, you might consider teaming up with another school to defray costs.
Children do not have to have read my books but it does make the whole experience more interesting for the students, if they have.