Thant is a very frustrating situation.I agree with Jeri P. Ive been a part of alot of toilet learning toddlers - once they have control over their bodies - there are few excuses to accidents when he or she was already mastered that area.
Reverting back to pull ups or diapers will only regress your child - so good job for not doing that! However - what to do when they CHOOSE to not use the toilet even though they have sat on it? Thats right - they made the choice - they can clean it up.
You see, cleaning it up is a negative consequence to their choice to not poop in the tiolet. Once a child has physical contol over their bowels (and every child gets that control at a different time), when they make a mess under normal circumstances - they can help clean it up. Although I would recomend leaving the cleaner/ disinfectant to mommy !
There are times when a normal child who has mastered the toilet can and will regress - seperation, deployment of a parent, divorce, moving, a new sibling, or any other major event - just to name a few.
I would advise a parent to never scold a child for honest accidents- just treat in a matter of fact way - help them get cleaned up - and have them help too. Then move on - embarassing them will only make it worse, and cause the child to have another accident. Also - rewarding with sweets can cause confusion later on ex:Good behavior = candy = risk for obesity and other health/ weight issues. Im not saying a jelly bean will be the demise to your toddler, its the pattern that is set in your childs brain, that is the problem. A sticker might be a good'reward' for having sucess at the toilet - JMO.
PM me if you have any questions regarding my advice - and good luck!