The actress, who has two boys Alexander and Samuel with husband Liev Schreiber, said that she would only consider having another child if it would definitely be a girl.
She told The Sun: "We try to turn our trips into a big adventure and not just hang around our hotel.
"I think children can have a more valuable education at their age by seeing the world as opposed to sitting in a room playing with blocks and finger painting.
"Two boys can be a lot to handle and sometimes you think it would be easier with two girls playing with their teas sets and dolls. But Liev loves having two boys.
"I suppose I might consider having another child - if someone could guarantee me it would be a girl."
Despite initially wanting to have children before she was 30, Watts left being a mother until later in life as she decided it was more important to have a successful career first.
She added: "I always wanted to have children when I was in my early 20s. Then, when I was living in Los Angeles, it was a question of trying to survive in the business and I wasn't in any state to even think about family.
"I also thought that I needed to establish myself in life and gain more wisdom and self-awareness."