Compare the Crisps: the unit-price detective game

Supermarkets print the answer to “which is better value?” on every shelf label — the price per 100g, in small type under the big price. Most adults never look at it. A child who learns to look has a genuine detective skill, and the shop you were doing anyway becomes the lesson.

How it works

1. Pick one product on your list. Crisps work beautifully, but cereal, yoghurt or biscuits do the same job. Something with a big brand, an own-brand and a multipack version nearby.
2. Show them the small print once. Point at the price per 100g and explain it in one sentence: it tells you what the same amount costs, so you can compare fairly even when the bags are different sizes.
3. Set the challenge. Two or three versions of the product. Which costs least per 100g? Let them hunt the labels themselves.
4. Check their answer together. The big pack or the own-brand usually wins, but not always — which is what makes it a real investigation rather than a trick.
5. Now the twist. Ask: so is the cheapest one the one we should buy? Sometimes yes. But maybe the huge bag would go stale, or nobody actually likes that flavour, or the dearer one is on offer this week only. Cheapest and best are not the same word.
6. Let them make the final call and put it in the trolley. Their decision, their reasoning, their crisps.

What usually happens

Once they’ve got it, they want to compare everything, and a twenty-minute shop becomes an hour. Cap it at one product per trip — it keeps the game special and the shop bearable.

Sooner or later they’ll catch a big pack that’s dearer per 100g than the small one. Supermarkets do this on purpose, and catching it feels wonderful. Let them be smug about it.