Our 2 year old (27 mo old) daughter has been trying to go potty on the toilet since she was 17 months old. Because we had a new baby on the way, we didn't want to aggressively potty train her. So she is able to go when she asks, but if she doesn't ask, we don't push it.
We put a potty chair in her room so that she could try to use the potty. She has had success peeing and pooping on that potty and the big potty with a potty seat.
However, today was the 2nd day this week that she has taken her diaper off and either peed the bed or peed and pooped on the floor. She wants to be in panties so badly. We thought to put her in pullups instead to see if that would work.
I have found that there are some people going through this because of jelousy. We do have a 4 month old, who needed a lot of attention as she was 12 weeks early. I have tried to help her go on the potty by allowing panties and pullups, however she wet those without telling me, and she peed on the couch.