The jokes from my 4 year old are moderately more amusing, not surprisingly. So as not to be outdone by her little sister, she delivered this one in Spanish:
Un ratoncito subio al elevador.
El operador le pregunto: ¿Que piso?
El ratoncito le dije: Pues...mi colita!
I retold this joke this morning to my highschool English class, and they laughed. I think though, that since they've never heard me speak in Spanish before, that part of their amusement was just listening to me do that.
Exam weeks differ from regular weeks though. Once you've administered yours, you can relax some, and let your kids relax some too...watch a movie, study for exams in other subjects, and sometimes, speak a little of the L1 without anybody getting upset about it. =)