Kensington Palace said that the duke and duchess didn't want to leave George at home for almost a month.
The royal trio will start their tour on April 7 in Wellington, New Zealand, where George is expected to make his first official appearance since his christening last year.
“It’s a tremendously exciting visit and I can tell you the Royal Highnesses are looking forward to it immensely,” William's private secretary, Miguel Head, said of the tour.
“I think the breadth and variety of things they are going to be seeing and the people they are going to be meeting has made them very enthusiastic about the visit,” Head added.
The royal family will also visit Sydney, Australia, the neighboring Blue Mountains, Queensland, Adelaide and Canberra.
Prince William last visited Australia in March 2011.