"I told her she is beautiful and that she's got a tiny little bump," volunteer Christie Osborne, 49, told reporters following Kate's royal visit.
"I asked when her baby is due and she said mid-to-end of April."
While Middleton revealed her due date, she did not reveal whether she is expecting a girls or a boy. It's possible that like the first time, she does not know.
That's one way to keep the secret from the entire world. Probably the only way. Also makes for quite a surprise one way or the other in the delivery room.
The due date puts her on track for a second baby in 21 months. Kate and husband Prince William welcomed Prince George in late July 2013.
As expected, Middleton was a hit with the children at the event.
She may forget she is pregnant sometimes but she never forgets to leave a lasting impression. She laughed as Ayo, a 3-year-old boy, said "ta-da!"
He presented her with a card made by some of the children.
After checking out the greeting, the 33-year-old marveled, "It's a very big card isn't it? What's on the front?" Ayo told the pregnant royal, "It's a flower!"
