Any mother whose young child has ever started crying uncontrollably, thrown a temper tantrum, or resorted to puppy-eyed begging when she dropped the child off at daycare or left them in the care of a babysitter has probably heard it ‒ "Oh, your child has separation anxiety?"
Nearly everyone has an idea about what separation anxiety means, and that is precisely because it is very common. Separation anxiety, fears and worries about being away from primary caregivers, is considered normal in children up to around 30 months of age, when children generally become more comfortable with a wider group of trusted adult carers. 
Is My Child Separation Disorder Developmentally Appropriate Or The Sign Of A Mental Disorder?
The most effective way to begin to understand whether your clingy child is displaying developmentally appropriate behavior or could be suffering from diagnosable separation anxiety is to consult the current version of the Diagnostic and Statistical Manual of Mental Disorders, the DSM-5 . It identifies the following diagnostic criteria, or signs that your child has separation anxiety disorder:
- Recurrent and excessive fear and anxiety surrounding separation from attachment figures (usually parents) — this could take the form of a child worrying that something bad will happen to you or them while you are away, or the fear that you will not come back.
- Persistent refusal to be away from attachment figures — or rather, when you make the executive decision that your child will be away from you for a while, clearly expressed resistance to going to daycare, school, or their grandparents' home, for instance. While it might be clear as daylight that this includes a refusal to sleep over somewhere, an inability to go to sleep without your presence, even in the child's own home, may also occur. This resistance can take the form of temper tantrums or begging you not to leave. Here, it is important to note that your child's anxiety may cause extremely oppositional (unpleasant, rude, angry) behavior, as well as the extreme sadness parents would generally expect. 
- Profound fear of being alone even in familiar settings such as the home.
- Nightmares about being separated from you.
- Anxiety-related physical complaints such as stomach aches, headaches, bedwetting, and vomiting, when physically separated from attachment figures or just thinking about it.
We're not talking about a child taking time to get used to daycare, school, or a new babysitter, but rather about severe and persistent existential anxiety. Note that, precisely because some degree of separation anxiety is normal in young children, it may be hard for you to get a diagnosis — and the help you need — if your child is displayed signs of SAD before reaching school age.  Hence, some advocacy may be required on your part if you have a toddler or preschooler with severe separation anxiety.
What Causes Separation Anxiety Disorder In Children?
Worldwide, anxiety disorders are thought to occur in five to 25 percent of children [see 1], with separation anxiety disorder accounting for approximately half of all those cases . If you think your child may be suffering from diagnosable separation anxiety, you are, in other words, by no means alone. The striking prevalence of this disorder does beg the question — what causes SAD? It is a question that you, as a parent, will also want an answer to.
Research indicates that both genetic  and environmental  factors contribute to the development of separation anxiety disorder. Low parental warmth, or on the other hand overprotective "helicopter parenting" that limits a child's developmentally appropriate independence [8, 9] are among these environmental factors. Both of these parental behaviors, in turn, can be the result of traumatic experiences and resulting post traumatic stress disorder — and incidentally, a mother with PTSD is another risk factor for separation anxiety disorder in children. 
This is of course easier said than done, but look at it like this — if you have compassion for your child, who may have a diagnosable mental health disorder, shouldn't you extend that same compassion to yourself, also? The focus should be on where to go from now, talking about which...
How Is Separation Anxiety Disorder In Children Treated?
Given the fact that data indicates that around a third of cases of clinical separation anxiety disorder persist into adulthood where it is left untreated , intervention is recommended for your child's anxiety as early as possible.
Research suggests that cognitive behavioral therapy, which usually lasts up to 12 weeks, is the most effective treatment for this kind of childhood anxiety, although we should note that data pertains mostly to children over seven years old . As a parent, you will also play a crucial role in helping your anxious child overcome their separation anxiety. You can expect parental therapy sessions focused on assisting your child in overcoming their anxiety. 
Anxiety medication isn't usually recommended in young children, and will be offered only to those who do not respond sufficiently to therapy and the new anxiety coping techniques parents will learn during their own counseling sessions. 
With the help of these treatments aimed at both anxious children and their parents, most children will overcome their anxiety and learn to be comfortable with spending time with non-parent caregivers.