Developmental milestones are specific tasks that most children are able to do within a certain age range. Your pediatrician uses these milestones to see how your child is developing. Each milestone has an age level, but in actuality, the age a child is when he reaches that milestone can vary quite a bit. Each child is unique, so keep that in mind when reading about these developmental milestones; you may find that your child hasn't reached a certain one yet, but he may have been early reaching another one.