Not sure about photographs. If the kid is recognisable ie not part of a large group, then it is always good to ask him, the parents if around, or the Team Manager (the Team Manager will be acting in loci parentis) if they have any objections.
They ARU have very tight restrictions on Players agents and talent scouts talking to the kids. There is an accreditation process and you can bet your bottom dollar that the Accredited Agents will be watching like hawks for any non-accredited types engaging with the kids. The tournament will be open to all to watch, even the dreaded "non-accredited" agents. They are just not allowed to approach the kids.
As long as you look like a "General Public" you should be OK.
Inside Shoulder, I note a couple of posts back that Uncle
Lee was looking for Match Reporters. Sounds like you may have volunteered yourself.
Edit: Spelling