The time frames seem off
I have read many of the more highly recommended baby book (Baby 411, What to Expect..., the AAP guide, Healthy Sleep habits, etc.), and we bought this book because my wife heard the authors give a talk. I have gotten quite frustrated reading the book because it seems that my 4.5 month son is only mapping to about 25% of the authors' stated developmental milestones. Yet in the aforementioned books, he's tracking between 50 and 75% to the stated milestones. Maybe babies in the Netherlands are just a lot more advanced than ours - but their developmental milestone calibration seems to be way off.