My dd started sitting on the potty/toilet from around 15 months we occasionally caught a we'd or poo and then at 28 months she woke from a day sleep and asked for her Dora undies ( which we had brought her 2 months earlier as an insentive). In one month we have had about 10 accidents but she pretty much went from nappies to undies in a day and only wears a night nappy now. She is in undies for day sleeps to.

I think it's never to early to get them used to it. With the flushing it down the toilet a get dd to do it and say buy wee.