I am strictly a knickers girl but call them pants with my 3yr old DD. Dunno why but 'knickers' seems a little bit too adult a word to use in relation to her.
But anyway, she takes them off wherever and whenever she can. Had a friend round today that hadn't seen in a long while and during conversation with her found my DD's knickers stuffed in the corner of the sofa where friend was sat. She must have seen them but was too polite to comment.
I also realised after friend had gone that she had been going to the loo all afternoon with DD's toilet seat still sat there on the loo. Bless her.