The Take That star revealed that his wife Ayda Field is "desperate" to have children.
Williams wed Field at his home in Los Angeles last August and in October he denied reports that the pair were trying for a baby, insisting that he's "putting it off for as long as possible".
However, the singer has confessed that he has now come around to the idea.
In an interview with Dutch TV show Rtl Boulevard, he said: "I thought that was part of the job. That's how it goes, isn't it? She desperately wants a child... I am terrified of that.
"I'm going to have to be [a good dad] and I will be because I will have to be. Yeah, I'm selfish. I enjoy doing what I want to do, whenever I want to do it. But on the [other hand], a baby comes into your life and you're forced to not have everything be about you, and that will be good for me."