Always business wear always no matter what the job
I think having a suit - if you can - is ideal
Certainly at least smart trousers or smart at least knee length skirt or dress
If wearing a skirt/dress cover legs or ensure legs in good order (no scratches etc)
Smart shoes, don't have to be heels, if heels don't go too high, I generally go flat because then no broken heel emergency! (I have form for this!)
Given the nature of the job:
Clean hands and short tidy nails (yes I know clean hands seems obvious but I used to hire in this area too and some candidates!!)
Hair clean and tidy (again seems obvious but...) tied up if longer than shoulder length
DON'T wear the rings! Trust me not for this role. What are the earrings like? I'd go with something small and tidy - again role specific - studs or small hoops nothing too fancy
If you have time/funds (can parents help?) black ballet pumps or loafers would be slightly better than vans.
Well done for thinking to get advice on this.
Hope it goes well for you. 