The till shows name, class and balance, so it is the right child. Tap an item, and it is taken off at once.
A limit per day and no sweets. The till says no to the wine gums, and once today's limit is used, it says no to the rest.
Same food, staff price. The till takes the price from the card, and the coffee that only staff can buy appears.
There is not enough for the dish of the day. A parent puts money on from their phone, and then it goes through.
The card has been lost, and the parents have blocked it. The till says no to everything, and the money stays on the card until it is opened again or a new card is made.