Grab a few clean jars, a sieve (or muslin if you have it) and some double cream and you are good to go. Outside or in, upstairs or down, even in the car!
Its so simple - Cream in the jar, lid tight, shake shake shake...
You can tell them the 3 stages of butter so they can feel in charge of the event.
1) it will go from creamy slooshing to solid
2) it will feel like you are shaking nothing
3) you will hear slooshing noises again.
When they hear the 3rd stage, tell them to look and see is there yellow butter in the jar. Cream or white is not butter! Any buttercup will tell you that!When the butter is present, get them to tip it onto a sieve or into some muslin and allow any milk to run off.
Mash with whatever flavourings you have handy... garlic or chili or both, salt and pepper, whatever you like - blitz in a mini chopper or processor and mash through the freshly made butter. Wrap in parchment and refridgerate until they are hungry... Funny how bread and butter sandwiches aren't snubbed when the butter has been made themselves!