I've got to admit, my children have spoken on the radio, both in ATC facilities and in the plane.
But we can all think of some seemingly innocent "kid to work day" stuff that very quickly got out of control. The Russian A300 that killed everybody in the far east is probably the best example (kid lost control sitting in the left seat in cruise, with daddy right behind him).
When Sully dropped his A320 in the Hudson, his actual May Day call was blocked by the controller transmitting. What if that had been a kid talking, and AWE1549 had a less satisfactory outcome?
It was cute, though. Loved the "adios amigo".