I know more about toilet training regression than I like to admit. If you are in the middle of it, I am really sorry. Here are some things that have worked for me and my kids. Nothing works every time, but eventually something will work whether it is one of these ideas or another.
Talking to a doctor
I knew there had to be a physical problem when my child was sitting on the toilet, and obviously holding it. The child now loves the doctor, because, "The doctor helps me get better." There is never a wrong time to talk to a trusted doctor. Toilet training regression can have multiple physical causes. Some of those causes require prescription medicine, so talking to the doctor is necessary. AskDrSears is a medical web-site that I have used, but nothing substitutes for a discussion with a live doctor.
Identifying an emotional cause
A new sibling, a sibling going to the hospital, and several moves have caused regressions in our household. In this case, I just tried to do the best I could to reassure my child. Usually, as the change was adjusted to, the regression naturally reversed, but not always.
Charge ahead, or take a break? A middle ground
Some people say that if you let them go back to diapers and start again, they will train faster the second time. It did not work that way for us. However, there are times when neither I nor the child can handle charging ahead.
A strategy which I found helpful was to partially revert to cloth diapers. If the child has success, they get to choose between diapers and underwear. If they have an accident, they wear diapers.
I think this works well for a list of reasons. First, disposable diapers keep the child dry, so they might have a hard time knowing when they have gone. Cloth diapers let them feel what just happened. Also, cloth diapers are less comfortable than underwear, so both my kids were pretty motivated to wear underwear.
My child sometimes chose diapers, and I realized that for a perfectionist temperament, the stress of needing to use the toilet was counter productive. Without the stress of a mess on carpet in a rented home, my responses to accidents were more appropriate. Sometimes the diaper wearing child would make it to the toilet and "earn" under wear. This strategy let the child feel in control. I think that was helpful in getting past some of the emotional struggle of regression. For us, it was the right amount of motivation, without the undue stress.
When our move caused a total regression, and I had left cloth diapers behind, I went to Green Mountain and bought six Indian pre-folds, a snappy, and two plastic covers. That is what you will need if you are starting just when you hope to finish. If you've never done cloth, ask for the information sheet, it's an excellent resource.
What other tactics would you add to a mom's bag of tricks for over coming toilet training regression?
Related posts: How to potty train: Before you actually start