Children between 5 and 6 can only have the Pfizer vaccine. 6-11 year olds can have either Pfizer or Moderna. Your child will require 2 doses, 8 weeks apart (but this can be brought forward to 3 weeks in specific circumstances).
More detailed information about the vaccine can be found in the ATAGI recommendation, and the Covid childhood vaccine government consent form.
If your child is aged 11 years and has the paediatric formulation for their first dose, and then turns 12 years of age before their second dose, they should have the adult Pfizer formulation as their second dose.
The Pfizer paediatric vaccine can be co-administered with other vaccines.