During pre-school, which usually goes from 3 to 5 – 6 years old, children’s minds experience an explosive transformation characterized by amazing changes in the way they think, they know, they memorise and communicate. They begin to compare, analyse and also find right solutions to problems. This process is called ‘Cognitive development’, which is characterised by milestones that represent important steps forward in a child's growth. When entering pre-school, children usually have already reached some of these milestones, although they might be taken as general ideas rather than a check-list, as some kids might be ahead and other a bit behind (Figure 2).

Figure  2.  Milestones development