The couple were on the second day of their Diamond Jubilee tour of Singapore, chatting with bystanders at the Gardens by the Bay park.
A teenager boldly asked the 30-year-old prince how many kids he'd like to have.
"Someone asked him how many children he would like to have, and he said he was thinking about having two," said a young woman at the event, in which 3000 people turned up to see the royal couple.
The news comes just as rumours swirl around Catherine possibly being pregnant. Some claim the Duchess of Cambridge's fashion choices are a bit spacier around the belly.
New York Daily News were quick to suggest that Kate "showed what may be a hint of a baby bump".
But the proof, apparently, was the 30-year-old princess' choice of drinking two glasses of water instead of wine when two toasts were made at an important dinner.
Could those little Willies be closer than expected? See if you can spot a bump in this clip of them in Singapore:
In pics: Cutest celebrity babies!