A thought which occurred when commencing a complete re-read

[justcarol67]

No: HPFGUIDX 99993

Phil wrote:
<snip>
How *did* the Dursleys know that the Potters had a small son if they
were so intent on ignoring their existance?

Indeed, how did Vernon know that Harry was "about the same age" as
Dudley?

Tana responded:
I personally presumed that even if she was ignored by her sister, Lily 
would have said SOMETHING about having a baby, maybe not directly to 
Petunia (maybe their parents were still alive? I Have no clue) But a baby 
is big enough news that even people ignoring you would probably have been 
told. Lily might have even TRIED to use it to get back in with her
sister? 
You have a baby, I have a baby, lets be friends again?
 
Carol adds:
Or Petunia sent Lily a birth announcement hoping for a gift and Lily
reciprocated (not for a gift, which she wouldn't be likely to receive,
but just to pass on the news)? Also, Petunia knew about Lily's
wedding, so I imagine she was invited (but didn't attend) or received
an announcement for that as well. And Lily could have kept up with
Petunia (the wedding and the baby) through the Muggle papers if she
chose to. And Petunia, being the nosy person she is, probably had ways
of finding out about Lily, too. Maybe Mrs. Figg was a longtime mutual
acquaintance!

Carol