2 ½ to 3 ½ Years:
Children at this age are still in a very egocentric stage of development. They see the world from their point of view and haven't reached a stage of empathy for others quite yet. Their play is still uncooperative and disorganized (until they reach around 4 years old). They are at a stage of parallel play. Which means they will play side by side even communicating with each other but not necessarily talking about the same thing (e.g. "my dad drives a big truck" and other child will answer "I had cereal for breakfast"). Notions of sharing and waiting for turns are still new or inexistent for most of them. Also, their attention span is very short and they will move from one activity to another very quickly.
3 ½ to 4 Years
Quickly, the child's attention span has grown, his speech has developed and interaction with other children becomes more interesting for him, recognizing feelings in others, thus developing empathy and a better understanding of others.
4 to 5 Years
Friendship becomes the new center of attention. Their play is now cooperative and organized. We see the appearance of role play and creativity is at its peak. What an exciting age! Children discover they have a direct impact on their environment and they recognize other people's feelings. They accept rules and routines; they learn to assume consequences and will emit opinions. It is a time many parents will also find challenging. Many children will test boundaries, empowered by their discovery of influence on others.