Er, we once told our 14 year old son we were 'going abroad', when we went to the Isle of Wight. We told him that we'd have to take passports and that they used a different currency (Grockles and Groats), plus they spoke a different language.
We sent him into a shop to buy something, we told him to ask very slowly how many Grockles and Groats to the Pound. I wonder if the shopkeeper remembers this. My son certainly hasn't forgotten........