Anne, in reply to your query, I will share an analogy which I sometimes
use with new moms with babies in our NICU.

"I don't expect you to see any milk at these first few pumping sessions.
 You might, but probably won't.  What we are doing is something like
this:  Think of your body as a factory.  In your brain is a production
manager(pituitary gland) who know s/he has to get a new product (milk)
out soon, but doesn't see the rush, or the need for a lot of the product
to be made right away.  The customer (your baby) is unable to talk to
the manager, so sends a representative (the pump) to knock on the
factory door (nipple stimulation).  The production manager realizes s/he
needs to respond to request for goods (milk), but only when the knocking
is consistence and hearty (regular, double pumping schedule), does s/he
send the workers (hormones) in sufficient numbers down to the production
line (alveoli) to make the product in the amount and the time frame the
representative is requesting.  Later, the customer (baby) will visit the
factory (breastfeeding), and insist on more product, more quickly
(better nipple stimulation through breastfeeding), and the production
manager will really "hop to" getting the workers to make more product
more quickly (milk)."

Then I explain, as needed, how milk supply increases with kangaroo care
and then more with actual breastfeeding.

This seems to help.  I know it is not absolutely accurate when
compared to what actually occurs physiologically, but it seems to hit
the basic concept in terms they can quickly grasp. I'm sure you will
hear other suggestions.  I, too, look forward to reading some.