My son just turned 3. He was toilet train when he was a few weeks old. Not by me but my mum. It takes a lot of patience!! My mum 's trick was to let him pee 5 mins after his feed. And once a day, half seat half carry (since he was only a month or so) to poo over the potty. It's all about conditioning.
By 6 mths old, he never pooed in his diaper since. He would give a "constipated" expression when he needed to poo and wait till someone brings him to the potty.
He was completely off diaper at 2, night diaper a few months later. He refused to wear diapers! There were a few occasions where he wet the bed, fortunately, for the past 6 mths, he would wake up to pee or when he keeps turning and tossing making noises at night (I am a light sleeper) I'll take him to the toilet with him protesting, but still he ends up peeing. Even when he was down w stomach flu few months back, he sat up, told me to bring him to the toilet where he vomited. The next night, he woke up again and had a bad episode of diarrhea.
My boy doesn't drink milk before bed. On occasions when he asks for milk, i give him only half his regular feed.
My daughter was completely off diaper on her first birthday and has never once wet the bed.
It takes loads of patience to keep taking the child to pee, and wait for him to pee. I passed this trick on to many parents at the playground and they all swear it works!