Found something on it. Doesn't seem quite as anti-Barrie as what I remember, but this might not be the same exact quote.
From: http://www.kidsreads.com/authors/au-mccaughrean-geraldine.asp
"What was your inspiration for the story of PETER PAN IN SCARLET?"
"I badly wanted to be true to Barrie's original book. Not to the cartoon version or the pantomime or the last movie, but to the 1911 book. So I read and reread PETER PAN AND WENDY, and tried to soak up something of Barrie's style and sense of humor and quirky style. I also wanted to create something distinctly my own. So what I went for was a literary counterpart --- the matching bookend --- same world, but somewhat altered. You see, I don't really share Barrie's gloomy take on life: That we are born happy and dwindle down to unhappiness as we get older, and that life is perfect at three, but sadder with each passing year. Nor do I think grown-ups are an altogether bad thing."
Sounds at least a little bit like McCaughrean should've been writing Hook & Jane. When I read "Literary counterpart", I somehow keep seeing "Counterpoint."