The final phase is the "relationship" phase, which occurs when the couple determines that they are fully committed to a long-term situation.
This is the phase in which you should introduce each other to your children, as the kids can feel a sense of permanency and stability.
However, remember that you have children now so it isn't quite the same as it was before.
Also consider the amount of time you have been divorced.
Children are not ready to have another parental figure thrown into the mix right after their parents' split.
Kids from divorced families have already experienced a loss and can get attached very quickly, so it is important to think about how the introduction will affect them.
Instead of determining when to introduce the kids based on the amount of time that has passed, think about it in terms of where you are in your relationship.