In Child Development (2002), the first volume in the Macmillan Psychology Reference Series, author Joan Ziegler Delahunt explains the difference, while John W. Santrock (2011) summarizes important motor milestones from birth to age twelve in his book with the same title:
…………………………………………………………………………………………………………. यो मुलुक सिंगापुर जस्तो बनिसकेको छैन मात्र राजनीतिक परिवर्तन...