Am YR1 teacher tasked with running 15-child (on rotation) Yr1-6 after school cookery club, all these suggestions good, as is Can't Cook Won't Cook (on tudou a lot). Hope experience might help:
Practically, I got utensils by appealing to parents for spare bowls, spoons etc. rather than having the PTA fork (excuse pun) out, on the understanding they'd be returned (nothing broken). The youngest children have ingredients weighed and chopped for them and put in ramikins, Ikea cups etc. so all they have to do is mix. I cook food that needs pre-cooking beforehand (we did a communal shepherd's pie with pre-cooked mince and potatoes, but they mashed, mixed and layered it). They break eggs into cups first so any shell can be removed, then tip them into bowls. You'll need to be well prepared so that participants' parents can check for culturally or medically unsuitable ingredients in advance, and be aware of some odd stuff (for instance, we had to get permission to do dippy with cake mix since it technically contains raw eggs).
Issues that I haven't yet resolved to my satisfaction are: smallish oven, and impracticality of cooking on hob even to show-group size is key here. The other is that an after school club means you'll have to fill anything over about 10 minutes cooking time with something.
I was a bit loathe to go as you did for all all cold food or quick assembled food (which tends to be only snacks or puddings) so sometimes the poor sods get stuff relevant to the food prepared-where it comes from, how farms work etc. for 10-20 minutes each time I want to cook something with a longish cooking time. We also spend cooking time thinking about what we've cooked and how it might make a meal or menu healthily (which sometimes gives hints about where to go next). I think that is educationally valid, and should be part of what 'cooking' is, but worry its tedious. If teachers are involved this sort of thing is something they might be able to help with this to allow you to extend cooking times a little.
IMO, it would be better as a lunchtime club or to take (especially that young) some time out of the afternoon with really-say at choosing time for Reception and YR1-not as an afterschool club, since that lets them prepare food and then do something else while it is cooked, picking it up at hometime. It also saves the school from the insurance burdens of having to have extra staff around to supervise you.