If you are PR or Australia government sponsored student, you child can go the state school where you are living. The teacher will arrange him/her to the right class according to his/her age, skills and knowledge. Some schools may arrange the child to special English language training class as well. You need to bring the child's passport and the rent agreement etc. The passport will proof the status of the child. The relativeship certificate is usually not needed, only if you are not the guardian of the child.