Eavesdropping

There's a conversation going on outside just now:

LS: Daddy's gone to work.  Mummies don't go to work.
BB: Some Mummies do, but not our Mummy.
LS: Mummy go work in da office
BB: but she doesn't go anywhere to work
LS: yeah.  Mummies don't go to work.
BB: Some Mummies do though.  Gran goes to work.
LS: Gran's not a mummy.
BB: Yes she is.   Well she was when Daddy was a baby and a boy.  That's before you were even born.
LS: (shocked tones) NO!
BB: it's true.  Daddy was a little boy one day, and that was before we were born.
LS: Is Gran Daddy's mummy?
BB: She is.  Amazing, isn't it!
LS: yeah!