Anmer Hall may need another nursery. Kate Middleton and Prince William, parents of George, 3, and 16-month-old Charlotte, “want a third baby soon,” a family friend reveals exclusively in the new issue of Us Weekly. “It would not surprise me if they were pregnant by Christmas.”

The Duke and Duchess of Cambridge are prepared to arrange their calendars accordingly. Should Kate, 34, become pregnant, the source says she and William, 34, will curtail their royal tours in 2017. After all, Kate suffered from hyperemesis gravidarum (a.k.a. acute morning sickness) with the first two pregnancies. The source says the royals would also be cautious because of the spreading Zika virus, which causes birth defects in unborn babies. (Until she's pregnant, it’s business as usual: They are due in Canada for an official visit from September 24 through October 1.)

The couple would be happy to remain home away from the spotlight. At the 10-bedroom mansion in Norfolk, “their kids are living as normal lives as possible,” says a Middleton family friend. There, George plays with Matchbox cars — “He’s obsessed with anything with an engine,” says a source — while Charlotte shadows Mom. “If Kate is in the study,” says the source, “Charlotte wants to be in the study.”

William and Kate are now eager to add to that idyllic family portrait. "I think they both would have been overwhelmed at the thought of a third child a year ago,” says the friend, “but now it sounds perfect. They've both always wanted a big family."

For more on the royals, pick up the new issue of Us Weekly, on stands now.

Want stories like these delivered straight to your inbox? Sign up now for the Us Weekly newsletter!