I actually put aside a few very clean (like new) underwear that my own son and daughter outgrew when they were a size 2, 3, 4 and I keep them clean and on hand just in case of severe emergencies. I usually write a note to the parent explaining that I borrowed them my 'extra' pairs and the parents usually thank me, wash them and send them back.

I have been in the same situation and wondered which route to go and felt bad about sticking a trained child back into pullups.

THe goods news is - that your dcparents will likely be packing spares tomorrow