With Christmas behind them and a new year on the horizon, Prince William is already planning a luxe vacation to celebrate wife Kate Middleton’s Jan. 9 birthday.

Life & Style reports the Duke of Cambridge, 37, is planning a mini-getaway for Middleton’s 38th birthday, with plans to bring along kids Prince George, Princess Charlotte and Prince Louis.

“Now, William wants to whisk their family away from it all on a no-expenses-spared trip to Mustique as a surprise for Kate. A big surprise!”

The source continued, “They’ll stay in a $15 million, seven-bedroom mansion with an infinity pool, private chef, screening room, gym and tennis court. William wants to ensure they get quality alone time as a couple, so he’s organizing spa treatments, a diving trip and surfing lessons for two.”

Apparently, there’s plenty for the children to do as well.

“George and Charlotte love Mustique — building sandcastles, swimming in the ocean, snorkeling and going on nature tours are just a few of their favorite activities,” the source shared. “And now that Louis is a bit older, he can get involved, too.”

William’s brother, Prince Harry, and wife Meghan Markle are currently vacationing themselves, spending the holidays with Markle’s mother in Canada.