In my experience there is no point in helping to toilet train a child until they are at an age where they show awareness of what is happening 'down there' and have the emotional maturity to allow you to guide and encourage. Let's talk about number ones and twos.
Using the potty is a cognitive experience for kids. There is little you can do, but wait for them to make the connection between their urge and the result. Each time you encouage a sit on the potty, be calm and PATIENT. Some chicky-babes are quicker than others. NEVER FORCE!
Potty training can be hindered if a parent uses coercion,threats or punishments to get the child to use the potty. In my experience, I have seen some very negative results when any of these techniques have been used. Let me share one story with you along those lines. A mother came to me one day and told me that her 3 year old was deliberately pooing into her pants and would then smear the poo everywhere, on the carpet, walls etc. Mum admitted having used all the negatives, as described above, to get her to use the potty or toilet and the little one had refused anyway. Now that the little one was older,smarter and could use 'revenge' behaviour, she did and continued to do so, much to the Mum's distress. The startegy was to get Mum to change her own reaction to it all and that took 2 to 3 weeks for it to work.
Incentives may well work for some, but I prefer that the child will gravitate to using the potty by themselves when parents use encouragement and take time to allow the child to do this. A child may well wee into a potty but may refuse to do a poo and prefer to use a nappy for that. I recommend to parents to allow the child to do so and in time the child gravitate to using the potty or toilet. A child will withdraw to a private spot and do the poo and come back for you to help change back into little nickers again. It really is a very private matter for the child, try not to make a fuss.
Remember, time is the key and some littlies will be quicker than others. Stay cool!