I don't think nurserys are allowed to stipulate that any more, Luce - you should check up with them - My friend was having a lot of probs training her little boy & in the end, she just sent him to nursery in pants, even though he was mostly having accidents and not going to the toilet .... he was trained in a week! Guess it was a combo of having different people "training" you & watching the other boys & girls doing it ..... don't worry ... either way, it will be fine ..... my DD was 2.8 yrs when we started her and she has only just stopped having one or two accidents a day, she is 3.5 yrs now, it has been a long old haul. Nursery didn't mind, as long as I sent her with a good supply of trousers and pants.
Hope Izzy settles well tonight and doesn't give you a bad night, Ange hon. xx