The first conversation I had with one of the children at school this morning went like this:
M: Hannah, my Mummy had to go quickly today cos she's gone to sell blood.
Hannah: (chuckling to self, knowing exactly what M meant - that Mummy was 'giving' blood)
Is she? Wow, that's interesting. Do you know why Mummy's giving blood?
M: Yes, it's for the old ladies whose blood drops out.
As always, the kids know exactly what they want to say and how to say it.