New each Tuesday. Although there seems to be an unspoken age of two years old for children to learn to use the toilet, two year olds are not always developmentally ready to toilet learn. First things first, don't bribe your kids with candy, television, or rewards to use the toilet. Bodily functions aren't easily bribed.
Bribery is never a good idea, for anything, including toilet learning.
It's much more positive for a child to learn to use the toilet because she is ready rather than because the parent is ready. It's important to remember that all kids do things at their own time and their own pace. You cannot push your child into being ready to toilet learn before she is ready. When she is ready she'll do it herself. Life as a parent will be a whole lot more enjoyable for you and your child if your time isn't spent with a power struggle over toilet learning.