Now, has Princess Kate given a hint they might be getting their wish?
She went shopping in one of her favorite stores, Amaia, in Chelsea, London, and was drawn to the girls' clothes, observers said.
"She was very interested," co-owner Segolene Tresca tells PEOPLE. "Every mum that comes in the shop, they look for boys' [clothes] but they always end up looking at the girls' stuff too. We all hope it's a little girl because it will be so cute, they will be like a little couple."
Ben Cawthra / Sipa USA
With royal watchers buzzing in the run-up to her April due date, some even fastened onto the fact that Kate, 33, wore baby pink for the service at Westminster Abbey to mark Commonwealth Day Monday.
British bookmakers are getting in on the act – with William Hill saying Tuesday that Elizabeth tops the charts of heavily backed names. Charlotte and Alexandra have also been high in the charts.
The couple have said that they don't know the sex, and William told President Obama in December that they are excitedly waiting for a surprise.
For Rupert Adams, spokesman at bookmakers William Hill, the chatter continues. "The money is all saying a girl – I don't know if people are looking at stats or just wishing it for the perfect family of a boy and a girl," he says.
Meanwhile, Kate – who after a difficult first trimester is now feeling and looking "marvelous," a friend says – is staying mum.