It all depends on the child. My son at 2 1/2 has been doing very well, and we introduced his potty chair to him when he was only a year or so. Everytime I would change his diaper, I would tell him about is potty chair and what he should do in it. But, we had problems actually getting him to do it. So, finally I decided to take him into the bathroom with me every time I had to go and it took just a few days. Since the arrival of his new baby sister he's slacked off just a bit and never tells me that he has to go potty, but slowly we are getting back in the habbit.
I think it's also important not to force them. Ask them if they would like to use the potty. Let them be in control. They will let you know when they are ready and will be trained before you know it!
Kara Kelso
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