All of a sudden your darling son does not want to wear anything that is pink or play with any toy that looks girly. This is because he is starting to understand the concept of gender. He is getting a better understanding of what is expected of boys and what is expected of girls. The story books that you have been reading to him or the older children that he has observed in the playground has helped form this understanding and differentiation.
What you need to know
Around the age of 2 years most children start being aware of the physical difference between a boy and a girl. Gender role behavior is an important concept that children this age start to learn and their games and behaviour will also be modeled as per this understanding.