I've just come back from a few days at a friend's place. Her DS2 is 20 months. And nearly toilet trained!
She isn't interested in early training, but her DS decided, a few weeks back, that pooing in the toilet was a good idea, so started asking for the loo when he needed a poo. He's had some "accidents" (he's still in nappies), but mostly gets to the loo in time.
While we were there, she forgot to put a nappy back on after a poo, so he went off to the loo when he needed a wee!
She's not training him, she's actually a bit boggled by the whole thing (as you would be!). But he seems interested in being clean and dry, so he's doing it.
Have other people's kids done this?