My kids are 5 and 8 and I had £15 this week to feed them until 28th. I had to explain to them the situation and fortunately they're old enough to understand, I bought porridge for breakfast and flour and eggs and basic vegetables like potatoes, carrots and some milk.
I do porridge for breakfast, they've had baked potatoes and beans for tea and French onion soup for lunch, all with home made bread to fill them up.
A cheap chicken can do a roast one day, chicken pie the next day and the carcass can make stock for soup the day after.
I plan on making a Spanish omelette one day too, filling and a bit different.
I know it's a real struggle and not having snacks for my kids is breaking my heart, but they actually have understood our situation really well and are happy to eat bread and butter if they feel the need to snack.
My DC2 is very fussy too, but I've told them straight if you don't eat what's on the table then that's it to the next meal, you're going to have a hungry tummy - seems to be working and I'm getting clean plates every time.
Good luck to you, it's a struggle I know, but I found I had quite a good stock of lentils, pasta etc in the cupboard and some fish and meat in the freezer so I know we're not going to starve. It's difficult though.
I've got a massive headache though because I've run out of coffee and won't be able to buy some more till pay day - caffeine withdrawal is not good.