The 31-year-old model and the chart-topping singer welcomed their first daughter, Luna, into the world in April this year - and John has revealed they plan on having an even bigger family in the future.
He shared: "It's a beautiful thing. We want to have a few more hopefully. Three or four. We'll play it by ear though."
The 37-year-old musician and Chrissy struggled with infertility for several years before they eventually turned their attention to IVF in order to conceive.
John said their doctor was never able to give them an answer as to why it "didn't work out naturally", but he explained that they did what they had to do as a couple in order to have a baby.
Speaking to Mr Porter's The Journal, John said: "We figured eventually we'd have to go into the doctor and see why it wasn't happening naturally.
"You know, sometimes it's just harder for some people than for others. We're just happy that we were able to do it with our doctor.
"He's never really told us that there was something specific that he could identify was the reason why it just didn't work out naturally. We did what we had to do."
Meanwhile, John recently got the cast of 'Sesame Street' to give his baby daughter Luna a cute shout out.
The 'Ordinary People' hitmaker was making a guest appearance on the programme and got the Muppets, including Big Bird and Elmo, to send a message to his seven-month-old baby girl.
In a clip posted on John's Instagram account, the Muppets say: "Hello Luna. We love you so much. You are so cute. Kiss, kiss."