Developmental Milestones are simply skills or behaviours that most children can perform by a certain age. What people forget to say in this simple definition, is that it isn’t a single specific age when a child reaches this milestone, but rather an age range. 

Typically milestones are divided into domains of development. They are Physical Development, Cognitive Development, Social Development and Emotional Development, although the last two are often listed together as Social and Emotional Development. More recently, various curriculum frameworks and experts in child development have started to refer to language and communication as a separate domain of development, whereas traditionally language development was discussed as a sub-domain within Cognitive Development.