Removable "key" for electric mains?

I have a small workshop/shed with some power tools and want to ensure that my kids cannot turn them on accidentally or on purpose without me present.

Is there some way to have a removable "key" that I can keep in the house which would physically disconnect all plug points in the shed?

I'm sure I've seen such removable connections for emergency use.

I'm not even sure what it's called to search for it.