What courses have you signed up for? SIMS/Arbor and Safeguarding courses can be completed in a day or 3 at most and would support your initial interview. Qualified first aider ( paediatric if EY's) is also advantageous. I appreciate there is a cost to these.
"I suppose because I have a child, a school seems an obvious option to explore to avoid childcare during the holidays".
Most sch admin roles require term time + 5/10 days, and training days, always in the holidays. You will need to look at the contract/job role you have applied for, to determine when you are actually required at work. Out of hours on occasion, to cover parents eves, open days/nights/ results days /plays and productions etc. Depending on the admin role, your head/ or trust will contract you in over holidays if your role dictates it. I work in schs, i have never yet left on time or had an "uninterrupted" holiday/half term.
Have a look at the job specs Op in order to prep yourself for the interviews. Research the roles and understand fully the nature and demands of the role you will be undertaking , the full responsibilities involved and the terminology used and what they all refer to . You will then be able to prepare yourself for the interviews.
With kindness Op, sch admin roles are so fast paced and varied, we simply do not have the capacity to sit training people up. You need to hit the ground running. Any advantage you can give yourself in terms of using sch software , experience of attendance, registers and safeguarding policies / procedures and all legislation in general , will help you as a start.