apart from asking for the mobile number, i would also spell it out "is there anything your child is allergic to, has your child got any medical conditions i need to be aware of?" - for the parents you don't know, but who choose to drop their child off with you. Safety first yada yada.

there are 31 kids in my child's prep class, so although i know some of the parents (on a basis level), there are many i've never spoken with.

Like AstroLady's example, bilby gets scared at things that some other kids her age, don't get scared about, so i would prefer to stay. Kids getting their face painted like Spiderman, or skulls etc, freaks her out.