The funnyman and his supermodel wife Lara Stone both want children, but David admitted he fears he won`t be strict enough with them and will be unable to discipline them.
He told Hello magazine: "I think the thing I`ll have to get good at is telling them off, because I`ve been around my nephews and my friends` kids where you don`t have to tell them off, you just do the fun bit.
I`ve noticed people being really good parents, it`s when they can be firm with their children at times if they do things that aren`t good for them."
Despite his fears, David can`t wait to become a father, because he loves being around kids.
He said: "We definitely want children. It`s a big responsibility so it`s easy to put it off. But then I`d imagine that there`s no perfect time - a time when everything`s tranquil in your life.
"I`m godfather to my nephew Eddie, who`s five. We didn`t have a religious ceremony so my title is something like `responsible adult.`
At least the adult part is true.
"My sister`s also just had another baby, Frankie, who`s about a month old, and loads of our friends have kids. I really love being around them."