I though I'd posted on this but it seems not... so you are all going to get the benefit of my wisdom now...
I do think that it is up to a parent to tell another adult in charge of their child if their child a) has any major food groups they do not eat (or is so fussy the list of things they DO eat is shorter than the list they do not and b) is anxious around food/food choices/selecting food.
We took 20+ Brownies on a sleepover for 24h. The first meal planned was lunch and the girls were offered sandwiches with a wide choice of fillings, fruit, and either yoghurt or crisps (memory fails me). One girl refused bread, fillings, and fruit and had about 1 bite of the other item. We learned from her school mates (she wasn't one of my own Pack) that she never eats bread and takes pasta for lunch at school (she herself was silent and refusing even to say "I don't like this", just shaking her head.)
Now I feel that not eating bread, ever, is a fairly major fussy behaviour. I'm not judging the parents for promoting/failing to stop this, but for failing to give us ANY information about this at all. No health or food allergy/intolerance information, no special needs information, and no additional food.
We had another girl with us who I knew well and who only eats bread or pasta and not much else. We knew this as parents had given us ample notice and information and offered to send extra food. But given this, and the fact that we had no girls with a known gluten intolerance, we decided to have sandwiches for lunch.
We had non-bread items for the tea but they all required cooking and we needed to leave pronto after lunch for a strenuous (for their age - it involved a hill, and it was a winter afternoon with early sunset) walk.
We left this girl behind with the cooks at the venue because she had eaten nothing, basically, after breakfast. Next day, her parents complained that they hadn't got what they paid for. Fine, we said, here's the cost of the walk back. £0. Next time tell us that your child does not eat a major staple food.
If you are catering for more than one child (especially when we are catering for more than 10!) you do have to assume that most commonly eaten foods are eaten by the children in your care, unless you are told otherwise. If a child's parent specifically tells you their child eats pizza, you're pretty reasonable in assuming that they do actually eat pizza!
And if as I say the list of foods they DO eat is shorter than the list they don't, then for goodness sake tell the adults in charge what your child will eat for breakfast - don't assume they have bread/cornflakes/Coco Pops in the house. Families don't all eat the same cereal/breakfast foods, and might easily run out of bread for toast.