Doesn't sound right coming from someone who had two perfectly healthy children, boy & girl, seemed well set up with family life & then had a third child. Nothing against anyone having three or even four children but maybe they're not the right person to be pontificating about this issue. I'll advised I would say, unless I've misunderstood him.
Inserted bit later:- There's something wrong about a person like Prince William - not talking about royal necessarily but someone reasonably well off - preaching to those who are so severely underprivileged, who often cannot access water never mind birth control. Many of those in third world countries don't want to keep on breeding and often lose children in infancy. We on the other hand, even those not earning much, would manage if they had an unplanned child - often known as 'a happy accident'. William needs to stand back and take stock - as do many others who preach the same. He's nice from what we can see & appears to genuinely care but saying what he said shows he has little idea.
Let's stand back and wait for the flack.