. . .when he says he wants Father Christmas to bring him 'a boat that goes up and down'?
It's not a submarine (I've asked).
I've not seen any adverts on the telly for anything like this.
One time he mentioned that he could take it in the bath, but that seems to be secondary.
He seems to have something very specific in mind and he doesn't tend to imagine toys, so I think this is something he's seen somehow, but he can't explain what it is.
This is just like the time when he kept telling me he wanted to go to a restaurant, and I'd ask which one, and he'd tell me 'Kids', which according to him was this marvellous place where everything was for kids and they had menus and brought lots of food to your table. About 2 weeks later we were driving and he started shouting, 'there's Kids!' - It was Pizza Hut, he'd gotten confused about the 'Kids Menu'.
So back to matter at hand, anyone seen any 'boats that go up and down' that aren't submarines?