Parting is not sweet sorrow for children — and adults — who can't tolerate being away from the people they love.
Young children hate to be separated from their parents. These fears appear toward the end of the first year, when they begin to sense that their parents will not always be with them and give signs of discomfort in the presence of people they don't know well. This normal separation anxiety peaks around age 2 and persists, slowly diminishing, through age 6 or 7.
If the fear of being apart from parents lasts for more than a month or persists in an older child and creates serious problems for the child or the family, it's called separation anxiety disorder. Fortunately, good treatments are available, and most families don't have to suffer long.